B.tech sem i engineering physics u ii chapter 2-laser
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Transcript of B.tech sem i engineering physics u ii chapter 2-laser
LASER
Light Amplification by Stimulated
Emission of Radiation
Course BTech
Subject Engineering Physics
Unit I
Chapter 2
Objectiveshellip
Introduction and understand the principle ofLASER
bull Light Amplification by Stimulated Emissionof Radiation
bull Absorption
bull Spontaneous Emission
bull Stimulated Emission
bull Population Inversion
bull Optical Pumping
Objectiveshellip
Characteristics or Properties of Laser Light
bull Coherence
bull High Intensity
bull High directionality
bull High monochromaticity
Laser light is highly powerful and it is
capable of propagating over long distances and
it is not easily absorbed by water
Introductionbull LASER
ldquoLight Amplification by StimulatedEmission of Radiationrdquo
bull MASER (1939 Towner)
ldquoMicrowave Amplification by StimulatedEmission of Radiationrdquo
bull Stimulated Emission - Einstein in 1917
bull Ruby Crystal LASER - Maiman California in1960
bull He-Ne LASER - Ali Javan in 1961
bull Diode LASER- Hall in 1962
Light having following Properties
Wavelength
Frequency
Amplitude
Phase
CoherenceIncoherence
Velocity
Direction
Absorption
bull E1 = Ground state
bull E2 = Excited State
bull E = hν (Photon Energy)
1
bull According to Bohrrsquos law atomic system is
characterized by discrete energy level
bull When atoms absorb or release energy it
transit upward or downward
bull Lower level E1 amp Excited level E2
bull So h ƒ = E2 ndash E1
bull The rate of absorption depends on no of
atoms N1 present in E1 amp spectral energy
density u(ƒ) of radiation
bull So P12 α N1 u(ƒ)
bull P12= B12N1 u(ƒ)
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Objectiveshellip
Introduction and understand the principle ofLASER
bull Light Amplification by Stimulated Emissionof Radiation
bull Absorption
bull Spontaneous Emission
bull Stimulated Emission
bull Population Inversion
bull Optical Pumping
Objectiveshellip
Characteristics or Properties of Laser Light
bull Coherence
bull High Intensity
bull High directionality
bull High monochromaticity
Laser light is highly powerful and it is
capable of propagating over long distances and
it is not easily absorbed by water
Introductionbull LASER
ldquoLight Amplification by StimulatedEmission of Radiationrdquo
bull MASER (1939 Towner)
ldquoMicrowave Amplification by StimulatedEmission of Radiationrdquo
bull Stimulated Emission - Einstein in 1917
bull Ruby Crystal LASER - Maiman California in1960
bull He-Ne LASER - Ali Javan in 1961
bull Diode LASER- Hall in 1962
Light having following Properties
Wavelength
Frequency
Amplitude
Phase
CoherenceIncoherence
Velocity
Direction
Absorption
bull E1 = Ground state
bull E2 = Excited State
bull E = hν (Photon Energy)
1
bull According to Bohrrsquos law atomic system is
characterized by discrete energy level
bull When atoms absorb or release energy it
transit upward or downward
bull Lower level E1 amp Excited level E2
bull So h ƒ = E2 ndash E1
bull The rate of absorption depends on no of
atoms N1 present in E1 amp spectral energy
density u(ƒ) of radiation
bull So P12 α N1 u(ƒ)
bull P12= B12N1 u(ƒ)
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Objectiveshellip
Characteristics or Properties of Laser Light
bull Coherence
bull High Intensity
bull High directionality
bull High monochromaticity
Laser light is highly powerful and it is
capable of propagating over long distances and
it is not easily absorbed by water
Introductionbull LASER
ldquoLight Amplification by StimulatedEmission of Radiationrdquo
bull MASER (1939 Towner)
ldquoMicrowave Amplification by StimulatedEmission of Radiationrdquo
bull Stimulated Emission - Einstein in 1917
bull Ruby Crystal LASER - Maiman California in1960
bull He-Ne LASER - Ali Javan in 1961
bull Diode LASER- Hall in 1962
Light having following Properties
Wavelength
Frequency
Amplitude
Phase
CoherenceIncoherence
Velocity
Direction
Absorption
bull E1 = Ground state
bull E2 = Excited State
bull E = hν (Photon Energy)
1
bull According to Bohrrsquos law atomic system is
characterized by discrete energy level
bull When atoms absorb or release energy it
transit upward or downward
bull Lower level E1 amp Excited level E2
bull So h ƒ = E2 ndash E1
bull The rate of absorption depends on no of
atoms N1 present in E1 amp spectral energy
density u(ƒ) of radiation
bull So P12 α N1 u(ƒ)
bull P12= B12N1 u(ƒ)
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Introductionbull LASER
ldquoLight Amplification by StimulatedEmission of Radiationrdquo
bull MASER (1939 Towner)
ldquoMicrowave Amplification by StimulatedEmission of Radiationrdquo
bull Stimulated Emission - Einstein in 1917
bull Ruby Crystal LASER - Maiman California in1960
bull He-Ne LASER - Ali Javan in 1961
bull Diode LASER- Hall in 1962
Light having following Properties
Wavelength
Frequency
Amplitude
Phase
CoherenceIncoherence
Velocity
Direction
Absorption
bull E1 = Ground state
bull E2 = Excited State
bull E = hν (Photon Energy)
1
bull According to Bohrrsquos law atomic system is
characterized by discrete energy level
bull When atoms absorb or release energy it
transit upward or downward
bull Lower level E1 amp Excited level E2
bull So h ƒ = E2 ndash E1
bull The rate of absorption depends on no of
atoms N1 present in E1 amp spectral energy
density u(ƒ) of radiation
bull So P12 α N1 u(ƒ)
bull P12= B12N1 u(ƒ)
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Light having following Properties
Wavelength
Frequency
Amplitude
Phase
CoherenceIncoherence
Velocity
Direction
Absorption
bull E1 = Ground state
bull E2 = Excited State
bull E = hν (Photon Energy)
1
bull According to Bohrrsquos law atomic system is
characterized by discrete energy level
bull When atoms absorb or release energy it
transit upward or downward
bull Lower level E1 amp Excited level E2
bull So h ƒ = E2 ndash E1
bull The rate of absorption depends on no of
atoms N1 present in E1 amp spectral energy
density u(ƒ) of radiation
bull So P12 α N1 u(ƒ)
bull P12= B12N1 u(ƒ)
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Absorption
bull E1 = Ground state
bull E2 = Excited State
bull E = hν (Photon Energy)
1
bull According to Bohrrsquos law atomic system is
characterized by discrete energy level
bull When atoms absorb or release energy it
transit upward or downward
bull Lower level E1 amp Excited level E2
bull So h ƒ = E2 ndash E1
bull The rate of absorption depends on no of
atoms N1 present in E1 amp spectral energy
density u(ƒ) of radiation
bull So P12 α N1 u(ƒ)
bull P12= B12N1 u(ƒ)
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
bull According to Bohrrsquos law atomic system is
characterized by discrete energy level
bull When atoms absorb or release energy it
transit upward or downward
bull Lower level E1 amp Excited level E2
bull So h ƒ = E2 ndash E1
bull The rate of absorption depends on no of
atoms N1 present in E1 amp spectral energy
density u(ƒ) of radiation
bull So P12 α N1 u(ƒ)
bull P12= B12N1 u(ƒ)
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Spontaneous Emission
bull E1 = Ground State
bull E2 = Excited State
bull E = E2 ndash E1
= ΔE
= hν
2
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
bull System having atoms in excited state
bull Goes to downward transition with emitting
photons hƒ = E1 ndash E2
bull Emission is random so if not in same phase
becomes incoherent
bull The transition depends on atoms in excited state
N2
P12(spont) α N2 = A21 N2
bull Where
A21 = Einstein coefficient for spontaneous
Emission we get Incoherent radiation forms heat
by light amplification of radiation by spontaneous
emission
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Stimulated Emission
3
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
bull System having atoms in excited state
bull Goes to downward transition with emitting photons
bull 2hƒ = E1 ndash E2 After applying photon energy hƒ
bull Emission is depends on energy density u(ƒ) amp No of
atoms in excited state N2
bull P12(stimul) α u(ƒ) N2 = B21 N2 u(ƒ)
bull Where B21 = Einstein coefficient for Stimulated
Emission
bull Thus one photon of energy hƒ stimulates two photons
of energy hƒ in same phase amp directions So we get
coherent light amplification of radiation by
stimulated emission
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Population Inversion
bull It is the process of increasing exited electrons in
higher energy levels
bull Due to this process the production of laser is
possible
bull The energy level between the ground state E1 (1st
level) and exited state E3 (3rd level) is known as
metastable state E2 (2nd level)
bull By optical pumping electrons from ground state
jumps to exited state by absorbing photons
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
bull The electrons remain only for 10-8 sec in exited
state E3 so most of them jumps back to the ground
state E1 by emitting photons But some of them
jumps to the metastable state E2
bull They (electron) stay in metastable state for more
then 10-3 sec
bull So electron density increases in metastable state
bull Thus the transitions are possible it takes more no
of electrons together and ν ndash (knew)12 photon beam is
produced which constitute laser beam
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Optical PumpingThere are no of techniques for pumping a
collection of atoms to an inverted state
bull Optical pumping
bull Electrical discharge
bull Direct conversion
When photon of blue green light incident onRuby crystal electrons from ground state absorbs andexited and jumps on higher energy state levels andcomes back to metastable state They increasepopulation of electrons in metastable state
This process is called optical pumping which isdone by flash tube
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Relation between Einsteinrsquos lsquoArsquo and lsquoBrsquo
coefficientsbull Einstein obtained a mathematical expression for the
existence of two different kinds of processes
(1) Spontaneous emission
(2) Stimulated emission
bull Consider all atoms r in thermal equilibrium at T
bull Radiation of freq ƒ amp energy density u(ƒ)
bull N1 amp N2 r atoms in E1 amp E2 respectively
bull In equilibrium absorption rates amp emission rates must be same
bull ie B12 N1 u(ƒ) = A21 N2+ B21 N2 u(ƒ)
A21 N2= u(ƒ) [B12N1 ndash B21N2]
So u(f) = [A21 N2 (B12 N1 ndash B21 N2)] ---------(1)
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
------------(2)
bull Boltzmann distribution law
------------(3)
bull So -----------(4)
bull But E2 ndash E1 = hf -----------(5)
bull So -----------(6)
21
21
12 1
21 2
( )
[ ]
ƒ
1
A
Bu
B N
B N
1
2
1 0
2 0
E kT
E kT
N N e
N N e
2 1( )1
2
E E kTNe
N
h 1
2
ƒ kTNe
N
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
---------- (7)
bull According to plankrsquos radiation formula
----------- (8)
bull Where B12 = B21 amp A21 B21 = ------------ (9)
bull So Ratio of spontaneous to stimulated emission
--------- (10)
21
21
ƒ12
21
h
ƒ
1
( )
[ ]kTe
A
Bu
B
B
3
3 ƒh
8 1( ) ( )
[ ]
ƒƒ
1kTu
c
h
e
3
3
8 ƒh
c
2 21 21
2 21 21
3
3
8
( ) ( ) ( )
ƒ
ƒ ƒ ƒ
N A A hR
B u B u ucN
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
bull So
--------- (11)
--------- (12)
bull So R = ---------- (13)
If hƒ ltlt kT in thermal equilibrium
then R = ltlt 1
bull hƒltltkT ndash Stimulated emission
ndashValid in microwave region (MASER)
bull hƒgtgtkT ndash Spontaneous emission
ndashValid in visible region incoherent
3
3
3
3
ƒh
8( )
8
ƒƒ
amp
ƒƒ
1
1( ) ( )
[ ]kT
h
uc
uR
h
e
c
ƒh 1[ ]kTe
ƒh 1[ ]kTe
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Types of LASER
There are three types of lasers
1 Solid Laser (Ruby Laser)
2 Liquid Laser
3 Gas Laser ( He ndash Ne Laser CO2 Laser)
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Ruby LaserhellipTo produce laser from solid Ruby crystal is
used
Ruby is an aluminum oxide crystal (Al2O3) in
which some of the aluminum atoms have been
replaced with Cr+3 chromium atoms (005 by
weight)
It was the first type of laser invented and was
first operated by Maiman in Research
Laboratories on 1960
Chromium gives ruby its characteristic pink or
red color by absorbing green and blue light
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Ruby LaserhellipFor a ruby laser a crystal of ruby is formed into
a cylinder The ruby laser is used as a pulsed
laser producing red light at 6943 Aring
4
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Ruby crystal is surrounded by xenon tube Rubycrystal is fully silvered at one side and partiallysilvered at the other end
A strong beam of blue green light is made to fall upon crystal from xenon tube and this light is absorbedby the crystal
Because of this many electrons from ground state ornormal state are raised to the excited state or higherstate and electron falls to metastable state
During this transition photon is not emitted butexcess energy of the electrons absorbed in crystallattice
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
5
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
As electron drops to metastable state they remain
there for certain time ~ 10-6 sec
Thus the incident blue green light from tube
increases the number of electron in metastable
state and then the population inversion can be
achieved
If a light of different frequency is allowed to fall
on this material the electrons move back and
forth between silvered ends of the crystal
While moving through they get stimulated and
exiced electrons radiate energy
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Thus radiation photon has the same frequency as
that of incident photon and is also in exactly same
phase
When the intensity of light beam is increased the
same process is repeated
Finally extremely intensified beam of light
energies from the semi silvered side of the crystal
This way it is possible to get extremely intensified
and coherent beam of light from the crystal This
beam is nothing but higher energetic beam ndash ie
LASER beam
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Applications of Ruby LaserhellipRuby lasers have declined in use with thediscovery of better lasing media They are still usedin a number of applications where short pulses ofred light are required Holographys around theworld produce holographic portraits with rubylasers in sizes up to a meter squared
Many non-destructive testing labs use ruby lasersto create holograms of large objects such asaircraft tires to look for weaknesses in the lining
Ruby lasers were used extensively in tattoo andhair removal
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Drawbacks of Ruby Laserhellipbull The laser requires high pumping power because
the laser transition terminates at the ground state
and more than half of ground state atoms must
be pumped to higher state to achieve population
inversion
bull The efficiency of ruby laser is very low because
only green component of the pumping light is
used while the rest of components are left unused
bull The laser output is not continues but occurs in
the form of pulses of microseconds duration
bull The defects due to crystalline imperfections are
also present in this laser
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Gaseous Laser (He ndash Ne Laser)A helium - neon laser usually called a He-Ne
laser is a type of small gas laser He-Ne lasers
have many industrial and scientific uses and are
often used in laboratory demonstrations of optics
He-Ne laser is an atomic laser which employs a
four-level pumping scheme
The active medium is a mixture of 10 parts of
helium to 1 part of neon
Neon atoms are centers and have energy levels
suitable for laser transitions while helium atoms
help efficient excitation of neon atoms
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
The most common wavelength is 6328 Aring These
lasers produced powers in the range 05 to 50
mW in the red portion of the visible spectrum
They have long operating life of the order of
50000 hrs
6
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Constructionhellip
It consists of a glass discharge tube of about
typically 30 cm long and 15 cm diameter
The tube is filled with a mixture of helium and
neon gases in the 101
Electrodes are provided in the tube to produce a
discharge in the gas
They are connected to a high voltage power
supply The tube is hermetically sealed with glass
windows oriented at Brewster angle to the tube
The cavity mirrors are arranged externally
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
WorkinghellipWhen the power is switched on a high voltage of
about 10 kV is applied across the gas
It is sufficient to ionize the gas
The electrons and ions are produced in the process
of discharge are accelerated toward the anode and
cathode respectively
The electron have a smaller mass they acquire a
higher velocity They transfer their kinetic energy to
helium atoms through inelastic collisions
The initial excitation effects only the helium atoms
They are in metastable state and cannot return in
ground state by the spontaneous emission
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
The excited helium atoms can return to the ground
state by transforming their energy to neon atoms
through collision This transformation take place when
two colliding atoms have initial energy state It is
called resonant transfer of energy
So the pumping mechanism of He-Ne Laser is when
the helium atom in the metastable state collides with
neon atom in the ground state the neon atom is excited
and the helium atom drops back to the ground state
The role of helium atom is thus to excite neon atom
and cause population inversion The probability of
energy transfer from helium atoms to neon atoms is
more as there are 10 atoms of helium per 1 neon atom
in gas mixture
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Without the Brewster windows the light output
is unpolarized because of it laser output to be
linearly polarized
7
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
When the excited Ne atom passes from metastable
state (3s) to lower level (2p) it emits photon of
wavelength 632 nm
This photon travels through the gas mixture
parallel to the axis of tube it is reflected back and
forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of
632nm with the stimulating photon
The stimulated transition from (3s) level to (2p)
level is laser transition
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Although 6328 Aring is standard wavelength of He-
Ne Laser other visible wavelengths 5430 Aring
(Green) 5940 Aring (yellow-orange) 6120 Aring (red-
orange) can also produced
Overall gain is very low and is typically about
0010 to 01
The laser is simple practical and less expensive
The Laser beam is highly collimated coherent
and monochromatic
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Applications of He-Ne Laserhellip
The Narrow red beam of He-Ne laser is used in
supermarkets to read bar codes
The He-Ne Laser is used in Holography in
producing the 3D images of objects
He-Ne lasers have many industrial and scientific
uses and are often used in laboratory
demonstrations of optics
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Semiconductor Laser (Diode Laser)
bull A semiconductor laser is a laser in which asemiconductor serves as a photon source
bull The most common semiconductor material thathas been used in lasers is gallium arsenide
bull Einsteinrsquos Photoelectric theory states that lightshould be understood as discrete lumps of energy(photons) and it takes only a single photon withhigh enough energy to knock an electron loosefrom the atom its bound to
bull Stimulated organized photon emission occurswhen two electrons with the same energy andphase meet The two photons leave with thesame frequency and direction
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
P type Semiconductors
bull In the compound GaAs each Ga atom has threeelectrons in its outermost shell of electrons andeach As atom has five
bull When a trace of an impurity element with twoouter electrons such as Zn (zinc) is added to thecrystal
bull The result is the shortage of one electron fromone of the pairs causing an imbalance in whichthere is a ldquoholerdquo for an electron but there is noelectron available
bull This forms a p-type semiconductor
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
N type Semiconductorsbull When a trace of an impurity element with six
outer electrons such as Se (selenium) is added
to a crystal of GaAs it provides on additional
electron which is not needed for the bonding
bull This electron can be free to move through the
crystal
bull Thus it provides a mechanism for electrical
conductivity
bull This type is called an n-type semiconductor
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
bull Under forward bias (the p-type side is made
positive) the majority carriers electrons in the n-
side holes in the p-side are injected across the
depletion region in both directions to create a
population inversion in a narrow active region
The light produced by radioactive recombination
across the band gap is confined in this active
region
8
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Application of Lasershellip
Laser beam is used to measure distances of sun
moon stars and satellites very accurately
It can be used for measuring velocity of light to
study spectrum of matters to study Raman
effect
It can be is used for increasing speed and
efficiency of computer
It is used for welding
It is used in biomedical science
It is used in 3D photography
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Application of Lasershellip It is used for communication T V transmission
to search the objects under sea
It can be used to predict earthquake
Laser tools are used in surgery
It is used for detection and treatment of
cancer
It is used to aline straight line for construction
of dam tunnels etc
It is used in holography
It is used in fiber optic communication
It is also used in military like LIDAR
It is used to accelerate some chemical reactions
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png
Image references links
1 https6postimgorg5mb8uomn1New_Picturepng
2 https6postimgorg3t8c6d1gdNew_Picture_1png
3 https6postimgorg72mrctpjxNew_Picture_2png
4 https6postimgorgj8gk0ytnhNew_Picture_3png
5 https6postimgorgo8e08wza5New_Picture_4png
6 https6postimgorgpby4kvjx9New_Picture_5png
7 https6postimgorgnf1egat99New_Picture_6png
8 https6postimgorgjjy0dqa3hNew_Picture_7png