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Transcript of [email protected] ENGR-45_Lec-13_Optical_Properties.ppt 1 Bruce Mayer, PE Engineering-45:...
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt1
Bruce Mayer, PE Engineering-45: Materials of Engineering
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engineering 45
OpticalOpticalPropertiesProperties
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt2
Bruce Mayer, PE Engineering-45: Materials of Engineering
Learning Goals – Optical PropsLearning Goals – Optical Props Learn How Light and Solid Materials Interact Why materials have characteristic colors Why some materials transparent
and others not Optical applications:
• Luminescence
• Photoconductivity
• Solar Cell
• Optical Fiber Communications
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt3
Bruce Mayer, PE Engineering-45: Materials of Engineering
Properties of Solid MaterialsProperties of Solid Materials
Mechanical: Characteristics of materials displayed when forces are applied to them.
Physical: Characteristics of materials that relate to the interaction of materials with various forms of energy.
Chemical: Material characteristics that relate to the structure of a material.
Dimensional: Size, shape, and finish
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt4
Bruce Mayer, PE Engineering-45: Materials of Engineering
Material PropertiesMaterial Properties Chemical Physical Mechanical Dimensional
Composition Melting Point Tensile properties Standard Shapes
Microstructure Thermal Toughness Standard Sizes
Phases Magnetic Ductility Surface Texture
Grain Size Electrical Fatigue Stability
Corrosion Optical Hardness Mfg. Tolerances
Crystallinity Acoustic Creep
Molecular Weight Gravimetric Compression
Flammability
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt5
Bruce Mayer, PE Engineering-45: Materials of Engineering
ElectroMagnetic RadiationElectroMagnetic Radiation Energy associated with Light, Radio Signals,
X-rays and Others is Transmitted as ElectroMagnetic (EM) Radiation (EMR)
Electromagnetic radiation Transmits energy in the form of a Sinusoidal wave Which Contains ELECTRICAL & MAGNETIC Field-Components
The EM waves Travel in Tandem, and are perpendicular to• Each Other • The Direction Of Propagation
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt6
Bruce Mayer, PE Engineering-45: Materials of Engineering
The EM SpectrumThe EM Spectrum EM Waves Cover a Wide Range of
WAVELENGTHS, , and FREQUENCIES, : miles→femtometers
“Light” is generally divided into Three Segments• UltraViolet: 0.001→0.35 µm
– NOT Visible, High in Energy• Visible: 0.35→0.7 µm
– A VERY Small Slice of the EM spectrum
• InfraRed: 0.7-1000 µm– Not Visible; carries “sensible”
energy (heat)
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt7
Bruce Mayer, PE Engineering-45: Materials of Engineering
EM Radiation QuantifiedEM Radiation Quantified All EM Waves
Travel at the Speed of Light, c
c is a Universal Constant with a value of 300 Mm/s (186 000 miles/sec)
c is related to the Electric & Magnetic Universal Constants
• Where (Recalling From Previous Lectures) 0 ELECTRIC
Permittivity of Free Space (a vacuum)
– µ0 MAGNETIC Permeability of Free Space (a vacuum)
001 c
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt8
Bruce Mayer, PE Engineering-45: Materials of Engineering
EM Radiation QuantifiedEM Radiation Quantified The Wavelength
and Frequency of EM waves are related thru c
• Where WaveLength in
meters per cycle Frequency in
Hertz (cycles/sec)
c
EM radiation has a Wave↔Particle Duality
The Energy, E, of a Light Particle
chE h • Where h
Planck’s Constant (6.63x10-34 J-s)
h is the PHOTON Energy
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt9
Bruce Mayer, PE Engineering-45: Materials of Engineering
EM-Solid InteractionEM-Solid Interaction Consider EM
Radiation with Intensity I0 (in W/m2) Impinging on a Solid
The EM-Solid interaction Alters the incident Beam by 3 possible Phenomena• The EM Beam can
be– Reflected
– Absorbed
– Transmitted
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt10
Bruce Mayer, PE Engineering-45: Materials of Engineering
EM-Solid Interaction contEM-Solid Interaction cont Mathematically
An Energy Balance on the Solid:• E-in = E-reflected +
E-absorbed + E-transmitted
TAR IIII 0
• Where all the IK are Intensities in W/sq-m
Now Divide E-Balance Eqn by I0
TAR 1
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt11
Bruce Mayer, PE Engineering-45: Materials of Engineering
EM-Solid Interaction cont.2EM-Solid Interaction cont.2
• Transparent → – T >> A+R
– Light Not Scattered
• Translucent→– T > A+R
– Light Scattered
0I RI
TI
AI• Where:
– R REFLECTANCE (IR/I0)
– A ABSORBANCE (IA/I0)
– T TRANSMITTANCE (IT/I0)
Using R, A, T, Classify EM-Solid Behavior• Opaque → T = 0
TAR 1
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt12
Bruce Mayer, PE Engineering-45: Materials of Engineering
Metals – Optical AbsorptionMetals – Optical Absorption Metals Interact with Light Thru QUANTIZED Photon
Absorption by Electrons
Energy of electron
Incident photon
filled states
unfilled states
E = h required
Io of E
nergy h
Metals have Very Closely Spaced e- Energy Levels
• Thus Almost ALL incident Photons are ABSORBED within about 100 nm of the surface
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt13
Bruce Mayer, PE Engineering-45: Materials of Engineering
Metals – Optical ReflectionMetals – Optical Reflection The Absorbed Energy is ReEmitted by e- “falling”
back to Lower Energy states Since Metals have Very
Closely Spaced e- Energy Levels The Light is emitted at many ’s
re-emitted photon from material surface
Energy of electron
filled states
unfilled states
E
IR “conducting” electron
• Thus Outgoing Light Looks About the Same as Incoming Light → High Reflectance
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt14
Bruce Mayer, PE Engineering-45: Materials of Engineering
Light Absorbtion/ReflectionLight Absorbtion/Reflection
Amount of NON-Reflected Light Absorbed by a Matl
For normally incident light passing into asolid having an index of refraction n:
e0IIT = absorption coefficient, cm-1
= sample thickness, cm = NonReflected incident
light intensity = transmitted light intensity
0I
TI
2
1
1tyreflectivi
s
s
n
nR
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt15
Bruce Mayer, PE Engineering-45: Materials of Engineering
Metals - ColorsMetals - Colors Metals also ABSORB
Some Photons• Dissipated as heat
Metals that Absorb few, orin broad-spectrum, reflect “WHITE” Light and Appear Silvery
Some Metals absorb Preferentially, and the Reflected Light is Colored due the absence of the Absorbed light• e.g., Cu Absorbs in the Violet-Blue; leaving
Reflected light rich in Orange-RedC
u B
ar
Sn
-Plated
Cu
Bar
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt16
Bruce Mayer, PE Engineering-45: Materials of Engineering
Total TransmissionTotal Transmission
Combining External and Internal Reflection, along with Beer’s Absorbtion Yields the TOTAL Transmission Eqn
eRIIT2
0 1
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt17
Bruce Mayer, PE Engineering-45: Materials of Engineering
Total-T ExampleTotal-T Example For the Situation at
Right Determine the thickness, d77, that will produce a total Transmittance of 77%
From Tab 21.1 Find Pyrex ns = 1.47
Next find R using Eqn (21.13)
13 mm
0I 086.0 IQuartzPyrex
23 mm
%621.3
147.1
147.1
1
122
R
n
nR
s
s
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt18
Bruce Mayer, PE Engineering-45: Materials of Engineering
Total-T ExampleTotal-T Example Recall total
Transmission Eq
Now Solve for β13 mm
0I 086.0 IQuartzPyrex
23 mm
eRIIT2
0 1
e
RI
IT2
0 1
20 1
lnRI
IT
20
1ln
R
IIT
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt19
Bruce Mayer, PE Engineering-45: Materials of Engineering
Total-T ExampleTotal-T Example Thus
Solving Total-T Eqn for the length Then d77
13 mm
0I 086.0 IQuartzPyrex
23 mm
meter350.3
2303621.01
86.0ln 2
mm
20
1ln
R
IIT mm 0.56
mm00335.0
03621.01
77.0ln
77
277
d
d
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt20
Bruce Mayer, PE Engineering-45: Materials of Engineering
NonMetals – Selective Absorb.NonMetals – Selective Absorb. In The Case of Materials with “Forbidden” Gaps in the
Band Structure, Absorption Occurs only if h>Egap
For TheseMaterials there is Very little ReEmission• The Material Color
Depends on the Width of the BandGap
incident photon energy h
Energy of electron
filled states
unfilled states
Egap
Io
blue light: h 3.3 ev
red light: h 1.8 ev
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt21
Bruce Mayer, PE Engineering-45: Materials of Engineering
Color Cases – BandGap MatlsColor Cases – BandGap Matls Egap < 1.8 eV
• ALL Visible Light Absorbed; Solid Appears Gray or Black in Color– e.g., Si with Egap = 1.1 eV
Egap > 3.3 eV
• NO Visible Light Absorbed; Solid Appears Clear and Transmissive– e.g., Diamond Egap = 5.45 eV, SiO2 Egap = 8-9 eV
1.8 eV < Egap < 3.3 eV
• Some Light is absorbed and Material has a color
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt22
Bruce Mayer, PE Engineering-45: Materials of Engineering
NonMetal ColorsNonMetal Colors Color determined by
sum of frequencies • transmitted light
• re-emitted light from electron transitions
e.g., Cadmium Sulfide (CdS)• Egap = 2.4eV
• Absorbs higher energy visible light (blue, violet),
CdS
• Red/yellow/orange is transmitted and gives it this color
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt23
Bruce Mayer, PE Engineering-45: Materials of Engineering
NonMetal Colors cont.NonMetal Colors cont. Ex: Ruby =
Sapphire (Al2O3) + 0.5-2 at% Cr2O3
• Sapphire is colorless (i.e., Egap > 3.1eV)
adding Cr2O3
• alters the band gap
• blue light is absorbed
• yellow/green is absorbed
• red is transmitted
Result: Ruby is deep Red in color
40
60
70
80
50
0.3 0.5 0.7 0.9
Transm
itta
nce
(%
)
Ruby
sapphire
wavelength, c/)(m)
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt24
Bruce Mayer, PE Engineering-45: Materials of Engineering
Wavelength vs. Band GapWavelength vs. Band Gap
Example: What is the maximum wavelength absorbed by Ge?
Find Ge BandGap: Eg = 0.67 eV
• Thus Need Ephoton = hc/λmax ≥ Eg
Use the Photon Energy Eqn:
mE
mE
hc
g
g
131eV11 Sifor :note
851J/eV10x601eV670
m/s10 x 3sJ10x62619
834
..
.).)(.(
))(.(
max
max
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt25
Bruce Mayer, PE Engineering-45: Materials of Engineering
Light RefractionLight Refraction When Light Encounters a Matter-Containing
Environment, it SLOWS DOWN Due to Interaction with Electrons
+no
transmitted light
transmitted light +
electron cloud distorts
Define the INDEX of REFRACTION, n
vOr
Matlin Light of SpdVacuumin Light of Spd
cn
n
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt26
Bruce Mayer, PE Engineering-45: Materials of Engineering
Light Refraction contLight Refraction cont The slowing of light in a Non-Vacuum Medium
Results in Refraction, or Bending of the light Path
Light Refracts per Snell’s Law :
2211 sinsin nn
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt27
Bruce Mayer, PE Engineering-45: Materials of Engineering
Refraction PhysicsRefraction Physics Recall Thus n
v
c n
Now the relations for v and c
001 c
1 v• Where ε & µ are
respectively the Permittivity & Permeability of the Material
Now Recall
rr
c n
00v
Most Matls are NOT magnetic → µr 1 • So
r n e.g. Germanium
• n = 3.97 → n2 = 15.76 r = 16.0 (very close)
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt28
Bruce Mayer, PE Engineering-45: Materials of Engineering
Application Application Luminescence Luminescence Based on EM Induced e− excitation, and then
Relaxation with Broad-Spectrum h Emission
e.g. fluorescent lamps
emitted light
h1+ h2+...
Energy of electron
filled states
unfilled states
Egap
Re-emissionOccurs
IncidentRadiation
h0
ElectronExcitation
Energy of electron
filled states
unfilled states
Egap
UV radiation
coating e.g.; -alumina,
doped w/ Europium
“white” light
glass
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt29
Bruce Mayer, PE Engineering-45: Materials of Engineering
Application Application PhotoConduction PhotoConduction h Absorption by NO-Junction SemiConductors
results in the Elevation of an e- to the Conduction Band Where it Can Carry an E-Field Driven Current
e.g. Cadmium Sulfide
semi conductor:
Energy of electron
filled states
unfilled states
Egap
+
-A. No incident radiation:
little current flow
Incident radiation
Energy of electron
filled states
unfilled states
EgapConducting e-
+
-B. Incident radiation: Increased current flow
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt30
Bruce Mayer, PE Engineering-45: Materials of Engineering
Application Application Si Solar Cell Si Solar Cell Recall The
PN Junction
Operation for Si Cell:• An incident PHOTON produces
HOLE-ELECTRON pair.• Typically 0.5-0.7 V potential
– Theoretical Max = 1.1 V (Egap).
• Current INCREASES with INCREASED Light INTENSITY– Need to Minimize Reflectance
n-type Si
p-type Sip-n junction
B-doped Si
Si
Si
Si SiB
hole
P
Si
Si
Si Si
conduction electron
P-doped Si
n
p
+ E
-
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt31
Bruce Mayer, PE Engineering-45: Materials of Engineering
Application – Heat MirrorApplication – Heat Mirror Natural SunLight is
Very Pleasant• However, In Sunny
Climes Windows that Admit Visible Light ALSO transmit InfraRed EM radiation that Heats the Building; increasing AirConditioning costs
Soln → “Heat” Mirror Window
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt32
Bruce Mayer, PE Engineering-45: Materials of Engineering
Application – Heat Mirror contApplication – Heat Mirror cont A Perfect Heat Mirror
Would • Transmit 100% of EM
radiation (light) in the visible 350-700 nm Wavelength range
• Reflect 100% of EMR over 700 nm
Heat Mirror Windows are Constructed from thin-film coated “window glass”
HM Film Stack → dielectric / metal / dielectric (D/M/D)• e.g., 300Å TiO2 /
130Å Ag / 300Å TiO2
http://www.cerac.com/pubs/cmn/cmn6_4.htm
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt33
Bruce Mayer, PE Engineering-45: Materials of Engineering
All Done for TodayAll Done for Today
TheSolar
Spectrum
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt34
Bruce Mayer, PE Engineering-45: Materials of Engineering
WhiteBoard WorkWhiteBoard Work
Derive Eqns
• 21.18d
T eI I 0
– Thick, Strongly Absorbing Medium of thickness d
• 21.19 dT eRI I 2
0 1
– Weakly Absorbing (transparent) medium with Reflection, R, and thickness d
[email protected] • ENGR-45_Lec-13_Optical_Properties.ppt35
Bruce Mayer, PE Engineering-45: Materials of Engineering
Heat MirrorHeat MirrorHot Miror (Heat Reflecting)
What - These "hot mirror" filters transmit the visible spectrum and reflect the infrared. At any specified angle of incidence, the average transmission is more than 93% from 425 to 675 nm. The average reflectance of our standard Hot Mirror is
more than 95% from 750 to 1150 nm.
Extended Hot Mirror: The average reflectance is more than 90% from 750 to 1600 nm.
Long IR Hot Mirror The average reflectance is more than 90% from 1700 to 3000 nm
Cold Mirror (Heat Transmitting)
These "cold mirror" filters reflect the visible spectrumand transmit heat (infrared). At any specified angle ofincidence, average reflectance is more that 95% from450 to 675 nm. Transmission is more than 85% from800 to 1200 nm.