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Paper on....

Laser Technology In Modern

Trend.Submitted by...

Mr.Mandar pathrikar

Mob no.9604725590

mandarpathrikar@yahoo.com

First Year Engineering

Imperial College Of Engineering & Research,

Gat No. 720/1&2, Wagholi, Nagar Road.

Pune-421 207

-:Under kind Guidance of:-

Mrs.Prof. prajakta dhole (electronics)

: Mr.waghchavre . (physics)

Abstract

Laser technology is the one of the best & pe globally spread type of technology.most of the device are made up of laser principle .In the x-ray this technique is used to stimulate the light for production .Laser is used in the medical as well as in the engineering field for various purpose.

Introduction

“LASER” we can simply define as “Light Amplification by stimulated emission of Radiation”

A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons.

The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation. The emitted laser light is notable for its high degree of spatial and temporal coherence, unattainable using other technologies.

Temporal (or longitudinal) coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively large distance (the coherence length) along the beam.

A beam produced by a thermal or other incoherent light source has an

instantaneous amplitude and phase which vary randomly with respect to time and position, and thus a very short coherence length.

History

In 1917, Albert Einstein established the theoretic foundations for the laser and the maser in the paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation); via a re-derivation of Max Planck’s law of radiation, conceptually based upon probability coefficients (Einstein coefficients) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation; in 1928,

In 1957, Charles Hard Townes and Arthur Leonard Schawlow, then at

Bell Labs, began a serious study of the infrared laser. As ideas developed, they abandoned infrared radiation to instead concentrate upon visible light.

1.HOW TO PRODUCE LASER

We know that on the theory of Einstein ,we can produce the laser waves.Laser is a device for producing a highly intense narrow beam of nearly

monochromatic light. Laser light can travel large distances without spreading and is capable of being focused to give enormous power density as high as 108 Watt/cm2. power density is the energy incident on unit area in one second.

  When  an electron from an orbit of higher energy (E2) jumps to an orbit of lower energy (E1), a photon of energy = (E2 – E1)= hv is emitted, where v is the frequency of the photon emitted. As this takes place spontaneously, it is called spontaneous emission.

If a photon of proper energy falls on an atom, it may be absorbed completely and an electron of the

atom in a lower energy state may be raised to a higher energy state. This process is called excitation.

Electron at initial energy level

In addition to the above two processes there is another process. An electron in a higher energy level may remain in that level for sometime. If another photon of energy hv=(E2 – E1) is incident on it, then the electron in the higher energy level is made to jump to the lower energy level emitting a photon of exactly the same frequency as the incident photon (figure). This type of emission is called stimulated emission.

Incident photon is the stimulating photon and the emitted one due to this, is the stimulated photon. The emitted photon is exactly in phase with the stimulating photon. This makes the laser action possible. Thus, two identical photons are produced in stimulated emission.

. The process of raising atoms from lower energy levels to higher energy levels is called population inversion. Population inversion is achieved by supplying energy from external

sources. The process of supplying energy from an external source, to achieve population inversion in a system, is called optical pumping.

Once population inversion is attained to sufficient extent, laser process is started by a stray photon of suitable energy.

Photon amplification takes place by stimulated emission. These photons are made to come out in the same direction as a narrow beam.

1.1 design of laser beam

Principal components:1. Gain medium2. Laser pumping energy3. High reflector4. Output coupler5. Laser beam

A laser consists of a gain medium inside a highly reflective optical cavity, as well as a means to supply energy to the gain medium. The gain medium is a material with properties that allow it to amplify light by stimulated emission. In its simplest form, a cavity consists of two

mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.

Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly. Part of the light that is between the mirrors (that is, within the cavity) passes through the partially transparent mirror and escapes as a beam of light.

The process of supplying the energy required for the amplification is called pumping. The energy is typically supplied as an electrical current or as light at a different wavelength. Such light may be provided by a flash lamp or perhaps another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.

1.2 Ruby laser tube

2. Types of laser

1.Gas laser

Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently. Gas lasers using many different gases have been built and used for many purposes. The helium-neon laser (HeNe) is able to operate at a number of different wavelengths, however the vast majority are engineered to lase at 633 nm; these relatively low cost but highly coherent lasers are extremely common in optical research and educational laboratories.

Commercial carbon dioxide (CO2) lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny spot. This emission is in the thermal infrared at 10.6 µm; such lasers are regularly used in industry for cutting and welding.

The efficiency of a CO2 laser is unusually high: over 10%. Argon-ion lasers can operate at a number of lasing transitions between 351 and 528.7 nm. Depending on the optical design one or more of these transitions can be lasing simultaneously; the most commonly used lines are 458 nm, 488 nm and 514.5 nm.

2. Chemical lasers

Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly. Such very high power

lasers are especially of interest to the military, however continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications. As examples, in the Hydrogen fluoride laser (2700-2900 nm) and the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride.

3. Solid-state lasers

A frequency-doubled green laser pointer, showing internal construction. Two AAA cells and electronics power the laser module (lower diagram) This contains a powerful 808 nm IR diode laser that optically pumps a Nd:YVO4 crystal inside a laser cavity. That laser produces 1064 nm (infrared) light which is mainly confined inside the resonator. Also inside the laser cavity, however, is a non-linear KTP crystal which causes frequency doubling, resulting in green light at 532 nm. The front mirror is transparent to this visible wavelength which is then expanded and collimated using two lenses (in this particular design).

Solid-state lasers use a crystalline or glass rod which is "doped" with ions that provide the required energy states. For example, the first working laser was a ruby laser, made from ruby (chromium-doped corundum). The population inversion is actually maintained in the "dopant", such as chromium or neodymium. These materials are pumped optically using a shorter wavelength than the lasing wavelength, often from a flashtube or from another laser.

It should be noted that "solid-state" in this sense refers to a crystal or glass, but this usage is distinct from the designation of "solid-state electronics" in referring to semiconductors. Semiconductor lasers (laser diodes) are pumped electrically and are thus not referred to as solid-state lasers. The class of solid-state lasers would, however, properly include fiber lasers in which dopants in the glass lase under optical pumping. But in practice these are simply referred to as "fiber lasers" with "solid-state" reserved for lasers using a solid rod of such a material.

3. Different applications need lasers with different output powers.

Lasers that produce a continuous beam or a series of short pulses can be compared on the basis of their average power. Lasers that produce pulses can also be characterized based on the peak power of each pulse. The peak power of a pulsed

laser is many orders of magnitude greater than its average power. The average output power is always less than the power consumed.

The continuous or average power required for some uses:

1-5 mW – laser pointers 5 mW – CD-ROM drive 5–10 mW – DVD player or

DVD-ROM drive 100 mW – High-speed CD-

RW burner 250 mW – Consumer DVD-

R burner 1 W – green laser in current

Holographic Versatile Disc prototype development

1–20 W – output of the majority of commercially available solid-state lasers used for micro machining

30–100 W – typical sealed CO2 surgical lasers[28]

100–3000 W – typical sealed CO2 lasers used in industrial laser cutting

1 kW – Output power expected to be achieved by a prototype 1 cm diode laser bar[29]

100 kW – Claimed output of a CO2 laser being developed by Northrop Grumman for military (weapon) applications.

3. MEDICAL APPILCATION OF LASER

In the medical field also there is very importance of laser technology.because this waves are highly coherent , monocromatic

&having highly focused wavelength from the graph we ca easily identify the flow of the blood capuscals

From the figure we can say that

The white blood cells have definite path & structure in the normal method this wave is not see as much as clear but with the laser theropy can show it in clear form.

As well as in the red blood carpuscals have low in number but presence of it we can see in accurate sinusoidle wave form.

4.Laser weapons

Laser beams are famously employed as weapon systems in science fiction, but actual laser weapons are still in the experimental stage.

The general idea of laser-beam weaponry is to hit a target with a train of brief pulses of light. The rapid evaporation and expansion of

the surface causes shockwaves. that damage the target.

The power needed to project a high-powered laser beam of this kind is beyond the limit of current mobile power technology thus favoring chemically powered gas dynamic lasers.

Lasers of all but the lowest powers can potentially be used as incapacitating weapons, through their ability to produce temporary or permanent vision loss in varying degrees when aimed at the eyes.

The degree, character, and duration of vision impairment caused by eye exposure to laser light varies with the power of the laser, the wavelength(s), the collimation of the beam, the exact orientation of the beam, and the duration of exposure

. The extreme handicap that laser-induced blindness represents makes the use of lasers even as non-lethal weapons morally controversial, and weapons designed to cause blindness have been banned by the

Protocol on Blinding Laser WeaponsIn the field of aviation, the hazards of exposure to ground-based lasers deliberately aimed at pilots have grown to the extent that aviation authorities have special procedures to deal with such hazards.[34]

On March 18, 2009 Northrop Grumman claimed that its engineers in Redondo Beach had successfully built and tested an electrically powered CO2 laser capable of producing a 100-kilowatt beam, powerful enough to destroy an airplane or a tank

. According to Brian Strickland, manager for the United States Army's Joint High Power Solid State Laser program, an electrically powered laser is capable of being mounted in an aircraft, ship, or other vehicle because it requires much less space for its supporting equipment than a chemical laser.

However the source of such a large electrical power in a mobile application remains unclear.

5. CNC LasersAt World Machinery we supply both new and used sheet metal fabrication machinery and equipment.

We specialise in laser cutting machines, CNC punch and turret presses, plasma and waterjet cutting machines along with pressbrakes

and sheetmetal guillotines. We can supply both new and used equipment anywhere in the world.

We have specialist engineers who can advise you on the suitability of all equipment for your application and our installation engineers will fully commission your equipment before handover when required and all machines can be seen under power if required at our extensive showroom and warehouse facilities.

5.1 Laser Cutting Methods

Depending on the material to be cut the cutting methods used differ :

Fusion Cutting ( high pressure cutting):

The material is fused by the energy of the laser beam.

The gas, in this case nitrogen at high pressure (10 to 20 bar), is used to drive out the molten material from the kerf.

The gas also protects the focusing from splashes

Oxidation Cutting (laser torch cutting):

The material is heated by the laser beam to combustion temperature.

The gas, in this case oxygen at a medium pressure (0.4 to 5 bar) is used to oxidize the material and to drive the slag out of the kerf.

The gas also protects the focusing optics from splashes.

The exothermic reaction of the oxygen with the material supplies a large part of the energy for the cutting process.

This cutting method is the quickest and is used for the economical cutting of carbon steels.

5.2 Parameters Affecting Laser Cutting

Laser power Pulse frequency Type and pressure of

cutting gas Distance between the

cutting nozzle and the work-piece

Cutting speed

Acceleration Material Work-piece surface Work-piece shape

1 = Laser beam

2 = Cutting gas

3 = Focusing lens

4 = Cutting head / nozzle

5 = Work-piece

6 = Blow-out molten mass

CONCLUSION

Advantages of laser technology

Laser technology has the following advantages:

High accuracy Excellent cut quality High processing speed Small kerf Very small heat-affected

zone compared to other thermal cutting processes

Very low application of heat, therefore minimum shrinkage of the cut material

It is possible to cut complex geometrical shapes, small holes, and beveled parts

Cutting and marking with the same tool

Cuts many types of materials No contact between the

material and machining tool (focusing head) and therefore no force is applied to the work-piece

Easy and fast control of the laser power over a wide range (1-100%) enables a power reduction on tight or narrow curves

The oxide layer is very thin and easily removed with laser torch cutting

High-pressure laser cutting with nitrogen enables oxide-free cutt

REFERENCES

1. MR. Waghchavre , F.E. physics lecturer & MSC (physics).

2. physics textbook of “ TEX-MAX”

3. Book written by V.K.Walekar,Dr.K.C. Nandi,& S.N.Shukla.