TERM PAPER

LASER, ACTION, EINSTEIN THEORY OF , TYPES, APPLICATIONS IN INDUSTRY & MEDICAL FIELD

SUBJECT: CURRENT, ELECTRICITY & MODERN PHYSICS

SUBJECT CODE: PHY-113

SUBMITTED TO: Dr. AMRITA SAXENA

SUBMITTED BY: JAGDEEP SINGH

SECTION: C7802

ROLL No.:RC7802A21

REG. No.: 10804440 CONTENTS

• Acknowledgement

• Introduction

• Laser action

• Einstein theory of laser

• Types of

1. Based on energy level

2. Based on the material used

• Applications

• Recent discoveries

• Recent applications

• References ACKNOWLEDGEMENT

For the completion of this term paper I would like to acknowledge my respected teacher Dr .AMRITA SAXENA who was always worthily helpful to help me in my queries in different aspects.

I would also like acknowledge my friends who helped me a lot in the completion f this and were always there at one call.

JAGDEEP SINGH INTRODUCTION

The name LASER is an acronym for Light Amplification by the Stimulated Emission of Radiation.

Light is really an electromagnetic wave. Each wave has brightness and color, and vibrates at a certain angle, so-called polarization. This is also true for laser light but it is more parallel than any other light source. Every part of the beam has (almost) the exact same direction and the beam will therefore diverge very little. With a good laser an object at a distance of 1 km (0.6 mile) can be illuminated with a dot about 60 mm (2.3 inches) in radius. As it is so parallel it can also be focused to very small diameters where the concentration of light energy becomes so great that you can cut, drill or turn with the beam. It also makes it possible to illuminate and examine very tiny details. It is this property that is used in surgical appliances and in CD players.

It can also be made very monochromic, so that just one light wavelength is present. This is not the case with ordinary light sources. White light contains all the colors in the spectrum, but even a colored light, such as a red LED (light emitting diode) contains a continuous interval of red wavelengths. On the other hand, laser emissions are not usually very strong when it comes to energy content. A very powerful laser of the kind that is used in a laser show does not give off more light than an ordinary streetlight; the difference is in how parallel it is.

Before the Laser there was the Maser In 1954, Charles Townes and Arthur Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation - the maser was invented before the (optical) laser. The technology is very close but does not use a visible light.

On March 24, 1959, Charles Townes and Arthur Schawlow were granted a patent for the maser. The maser was used to amplify radio signals and as an ultrasensitive detector for space research.

In 1958, Charles Townes and Arthur Schawlow theorized and published papers about a visible laser, an invention that would use and/or visible spectrum light, however, they did not proceed with any research at the time.

Many different materials can be used as lasers. Some, like the , emit short pulses of laser light. Others, like helium-neon gas lasers or liquid dye lasers emit a continuous beam of light. LASER ACTION

Lasers are possible because of the way light interacts with electrons. Electrons exist at specific energy levels or states characteristic of that particular atom or molecule. The energy levels can be imagined as rings or orbits around a nucleus. Electrons in outer rings are at higher energy levels than those in inner rings. Electrons can be bumped up to higher energy levels by the injection of energy-for example, by a flash of light. When an electron drops from an outer to an inner level, "excess" energy is given off as light. The wavelength or color of the emitted light is precisely related to the amount of energy released. Depending on the particular lasing material being used, specific wavelengths of light are absorbed (to energize or excite the electrons) and specific wavelengths are emitted (when the electrons fall back to their initial level).

In a cylinder a fully reflecting mirror is placed on one end and a partially reflecting mirror on the other. A high-intensity lamp is spiraled around the ruby cylinder to provide a flash of white light that triggers the laser action. The green and blue wavelengths in the flash excite electrons in the atoms to a higher energy level. Upon returning to their normal state, the electrons emit their characteristic ruby-red light. The mirrors reflect some of this light back and forth inside the ruby crystal, stimulating other excited chromium atoms to produce more red light, until the light pulse builds up to high power and drains the energy stored in the crystal. High-voltage electricity causes the quartz flash tube to emit an intense burst of light, exciting some of the atoms in the ruby crystal to higher energy levels. At a specific energy level, some atoms emit particles of light called photons. At first the photons are emitted in all directions. Photons from one atom stimulate emission of photons from other atoms and the light intensity is rapidly amplified. Mirrors at each end reflect the photons back and forth, continuing this process of stimulated emission and amplification. The photons leave through the partially silvered mirror at one end. This is laser light. EINSTEIN THEORY OF LASER

Although Einstein did not invent the laser his work laid the foundation. It was Einstein who pointed out that stimulated emission of radiation could occur along with spontaneous emission & absorption. He used his photon mathematics to examine the case of a large collection of atoms full of excess energy and ready to emit a photon at some random time in a random direction. If a stray photon passes by, then the atoms are stimulated by its presence to emit their photons early. More remarkably, the emitted photons go in the same direction and have exactly the same frequency as the original photon ! Later, as the small crowd of identical photons moves through the rest of the atoms, more and more photons will leave their atoms early to join in the subatomic parade.

All it took to invent the laser was for someone to find the right kind of atoms and to add reflecting mirrors to help the stimulated emission along .The acronym LASER means Light Amplification by (using Einstein's ideas about) Stimulated Emission of Radiation.

Stimulated Emission

Normally atoms and molecules emit light at more or less random times and in random directions and phases. All light created in normal light sources, such as bulbs, candles, neon tubes and even the sun is generated in this way.

If energy is stored in the atom and light of the correct wavelength passes close by something else can happen. The atom emits light that is totally synchronous with the passing light. This means that the passing light has been amplified which is necessary for the oscillation taking place between the mirrors in a laser.

Light is normally emitted from atoms or molecules that meet with two conditions. - They have stored energy originating from heat or previous absorption of light - A time has passed since the energy was stored Light emitted in this way goes in random directions, with random phases and at random times.

Albert Einstein predicted early in the 1900s that there is also another way for light to be emitted. It can amplify a passing beam, provided three conditions are met: - Energy is stored in the atom (same as above) - Light passes close enough to the atom before the time has expired and the light is emitted in the random fashion described above - The passing light has a wavelength suitable for the atom. The process taking place in this case is called Stimulated Emission, which, together with feedback in a resonant cavity between mirrors, forms the conditions for laser.

TYPES OF LASER

• ON THE BASIS OF ENERGY LEVEL

1. Two level: In this photon from mata stable state jumps to second level on excitation 2. Three level: In this photon from mata stable state jumps to third level on excitation 3. Four level: In this photon from mata stable state jumps to fourth level on excitation ON THE BASIS OF MATERIAL USED

GAS LASERS

Gas laser

Laser Operation medium Pump source Applications and notes wavelength(s) and type

632.8 nm (543.5 nm, Interferometry, holography, Helium- 593.9 nm, 611.8 nm, Electrical , barcode scanning, neon laser 1.1523 μm, 1.52 μm, discharge alignment, optical demonstrations. 3.3913 μm)

454.6 nm, 488.0 nm, 514.5 nm (351 nm, 363.8, 457.9 nm, 465.8 Retinal phototherapy (for diabetes), Argon nm, 476.5 nm, 472.7 Electrical lithography, confocal laser nm, 528.7 nm, also discharge microscopy,spectroscopy pumping frequency doubled to other lasers. provide 244 nm, 257 nm)

Krypton 416 nm, 530.9 nm, Electrical Scientific research, mixed with laser 568.2 nm, 647.1 nm, argon to create "white-light" lasers, 676.4 nm, 752.5 nm, discharge light shows. 799.3 nm

Many lines throughout Xenon ion visible spectrum Electrical Scientific research. laser extending into the UV discharge and IR.

Pumping of dye lasers, measuring air pollution, scientific research. Nitrogen Electrical Nitrogen lasers can operate 337.1 nm laser discharge superradiantly (without a cavity). Amateur laser construction. See TEA laser

Transverse (high Carbon power) or Material processing (cutting, dioxide 10.6 μm, (9.4 μm) longitudinal (low welding, etc.), surgery. laser power) electrical discharge

Carbon Material processing (engraving, 2.6 to 4 μm, 4.8 to 8.3 Electrical monoxide welding, etc.), photoacoustic μm discharge laser spectroscopy.

Excimer 193 nm (ArF), 248 nm Ultraviolet lithography for recombination via (KrF), 308 nm (XeCl), semiconductor manufacturing, laser electrical 353 nm (XeF) , LASIK. discharge

CHEMICAL LASERS

Chemical laser

Used as directed-energy weapons. Laser gain Operation medium and Pump source Applications and notes wavelength(s) type

Used in research for laser 2.7 to 2.9 μm for in a weaponry by the U.S. DOD, Hydrogen Hydrogen fluoride burning jet of ethylene operated in fluoride laser (<80% Atmospheric and nitrogen trifluoride mode, can have power in the transmittance) (NF ) 3 megawatt range.

~3800 nm (3.6 to MIRACL, Pulsed Energy Deuterium 4.2 μm) (~90% chemical reaction Projectile & Tactical High fluoride laser Atm. transmittance) Energy Laser

Laser weaponry, scientific and materials research, laser COIL 1.315 μm (<70% Chemical reaction in a jet used in the U.S. military's (Chemical Atmospheric of singlet delta oxygen Airborne laser, operated in oxygen- transmittance) and iodine continuous wave mode, can iodine laser) have power in the megawatt range.

Chemical reaction of chlorine atoms with gaseous hydrazoic acid, Agil (All 1.315 μm (<70% resulting in excited Scientific, weaponry, gas-phase Atmospheric molecules of nitrogen aerospace. iodine laser) transmittance) chloride, which then pass their energy to the iodine atoms.

DYE LASER

Laser gain Pump medium Operation wavelength(s) Applications and notes source and type

Dye lasers 390-435 nm (stilbene), 460- Other laser, Research, spectroscopy, 515 nm (coumarin 102), 570- birthmark removal, isotope separation. The tuning range of 640 nm (rhodamine 6G), flashlamp the laser depends on which dye is many others used.

METAL-VAPOR LASERS

Laser gain Operation medium and Pump source Applications and notes wavelength(s) type

Printing and typesetting Helium- applications, fluorescence cadmium 441.563 nm, 325 excitation examination (ie. in U.S. (HeCd) metal- nm paper currency printing), scientific vapor laser research.

Helium- mercury Rare, scientific research, amateur 567 nm, 615 nm (HeHg) metal- Electrical laser construction. vapor laser discharge in metal vapor mixed with helium buffer gas. Helium- up to 24 selenium wavelengths Rare, scientific research, amateur (HeSe) metal- between red and laser construction. vapor laser UV

Helium-silver (HeAg) metal- 224.3 Scientific research vapor laser

Electrical Neon-copper discharge in metal (NeCu) metal- 248.6 Scientific research vapor mixed with vapor laser neon buffer gas.

Copper vapor 510.6 nm, 578.2 Electrical Dermatological uses, high speed laser nm discharge photography, pump for dye lasers. Gold vapor Rare, dermatological and 627 nm laser photodynamic therapy uses.

SOLID-STATE LASER

Laser gain medium Operation Pump source Applications and notes and type wavelength(s)

Holography, tattoo removal. The Ruby laser 694.3 nm Flashlamp first type of visible light laser invented; May 1960.

Material processing, rangefinding, laser target designation, surgery, research, pumping other lasers (combined with frequency 1.064 μm, (1.32 Flashlamp, Nd:YAG laser doubling to produce a green 532 μm) nm beam). One of the most common high power lasers. Usually pulsed (down to fractions of a nanosecond)

Flashlamp, Er:YAG laser 2.94 μm Periodontal scaling, Dentistry laser diode

Mostly used for pulsed pumping of Neodymium YLF 1.047 and 1.053 Flashlamp, certain types of pulsed Ti:sapphire (Nd:YLF) solid-state μm laser diode lasers, combined with frequency laser doubling.

Neodymium doped 1.064 μm laser diode Mostly used for continuous Yttrium pumping of mode-locked orthovanadate Ti:sapphire or dye lasers, in (Nd:YVO4) laser combination with frequency doubling. Also used pulsed for marking and micromachining. A frequency doubled nd:YVO4 laser is also the normal way of making a green .

Nd:YCOB is a so called "self- frequency doubling" or SFD laser Neodymium doped material which is both capable of ~1.060 μm yttrium calcium lasing and which has nonlinear (~530 nm at oxoborate laser diode characteristics suitable for second second Nd: Y Ca O(BO ) or . Such 4 3 3 harmonic) simply Nd:YCOB materials have the potential to simplify the design of high brightness green lasers.

Used in extremely high power (terawatt scale), high energy ~1.062 μm (megajoules) multiple beam (Silicate Neodymium glass Flashlamp, systems for inertial confinement glasses), ~1.054 (Nd:Glass) laser laser diode fusion. Nd:Glass lasers are usually μm (Phosphate frequency tripled to the third glasses) harmonic at 351 nm in laser fusion devices.

Spectroscopy, LIDAR, research. This material is often used in highly-tunable mode-locked Titanium sapphire 650-1100 nm Other laser infrared lasers to produce ultrashort (Ti:sapphire) laser pulses and in amplifier lasers to produce ultrashort and ultra-intense pulses.

Thulium YAG 2.0 μm Laser diode LIDAR. (Tm:YAG) laser

Optical refrigeration, materials Ytterbium YAG Laser diode, processing, ultrashort pulse 1.03 μm (Yb:YAG) laser flashlamp research, multiphoton microscopy, LIDAR.

Ytterbium: O (glass 2 3 1.03 μm Laser diode ultrashort pulse research, [3] or ceramics) laser Fiber version is capable of producing several-kilowatt continuous power, having ~70- 80% optical-to-optical and ~25% electrical-to-optical efficiency. Ytterbium doped Material processing: cutting, glass laser (rod, 1. μm Laser diode. welding, marking; nonlinear fiber plate/chip, and fiber) optics: broadband fiber- nonlinearity based sources, pump for fiber Raman lasers; distributed Raman amplification pump for telecommunications.

Holmium YAG Tissue ablation, kidney stone 2.1 μm Laser diode (Ho:YAG) laser removal, dentistry.

Frequency quadrupled Cerium doped Nd:YAG laser lithium strontium(or pumped, Remote atmospheric sensing, calcium) aluminum ~280 to 316 nm LIDAR, optics research. fluoride (Ce:LiSAF, pumped, Ce:LiCAF) pumped.

Laser material is radioactive. Once Promethium 147 demonstrated in use at LLNL in doped phosphate 933 nm, 1098 ?? 1987, room temperature 4 level glass (147Pm+3:Glass) nm lasing in 147Pm doped into a lead- solid-state laser indium-phosphate glass étalon.

Flashlamp, Chromium doped Typically tuned laser diode, Dermatological uses, LIDAR, laser chrysoberyl in the range of mercury arc machining. (alexandrite) laser 700 to 820 nm (for CW mode operation)

Erbium doped and 1.53-1.56 μm Laser diode These are made in rod, plate/chip, erbium-ytterbium and optical fiber form. Erbium codoped glass lasers doped fibers are commonly used as optical amplifiers for telecommunications.

First 4-level solid state laser (November 1960) developed by Trivalent uranium Peter Sorokin and Mirek Stevenson doped calcium 2.5 μm Flashlamp at IBM research labs, second laser fluoride (U:CaF ) 2 invented overall (after Maiman's solid-state laser ruby laser), liquid helium cooled, unused today. [1]

Divalent samarium Also invented by Peter Sorokin and doped calcium Mirek Stevenson at IBM research 708.5 nm Flashlamp fluoride (Sm:CaF2) labs, early 1961. Liquid helium laser cooled, unused today. [2]

F-center laser. 2.3-3.3 μm Spectroscopy

SEMICONDUCTOR LASER

Laser diode

Laser gain Operation Pump medium and Applications and notes wavelength(s) source type

Semiconductor 0.4-20 μm, Electrical Telecommunications, holography, laser diode depending on current printing, weapons, machining, welding, (general active region pump sources for other lasers. information) material.

GaN 0.4 μm Optical discs.

AlGaAs 0.63-0.9 μm Optical discs, laser pointers, data communications. 780 nm player laser is the most common laser type in the world. Solid-state , machining, medical. Telecommunications, solid-state laser InGaAsP 1.0-2.1 μm pumping, machining, medical.. lead salt 3-20 μm

Vertical cavity 850 - 1500 nm, surface emitting depending on Telecommunications laser (VCSEL) material

Research,Future applications may Quantum cascade Mid-infrared to include collision-avoidance radar, laser far-infrared. industrial-process control and medical diagnostics such as breath analyzers.

Hybrid silicon Mid-infrared Research laser

OTHER TYPES OF LASERS

Laser gain Operation medium and Pump source Applications and notes wavelength(s) type

A broad wavelength range (about 100 nm - Free electron several mm); one relativistic atmospheric research, material laser free electron laser electron beam science, medical applications. may be tunable over a wavelength range

Gas dynamic Several lines Spin state Military applications; can laser around 10.5 um; population operate in CW mode at several other frequencies inversion in megawatts optical power. may be possible with different gas molecules caused mixtures by supersonic adiabatic expansion of mixture of nitrogen and carbon dioxide

Lasing in ultra-hot First demonstration of efficient samarium plasma "saturated" operation of a sub– formed by double 10 nm X-ray laser, possible pulse terawatt applications in high resolution scale irradiation "Nickel-like" X-rays at 7.3 nm microscopy and holography, fluences created Samarium laser wavelength operation is close to the "water by Rutherford window" at 2.2 to 4.4 nm where Appleton observation of DNA structure Laboratory's and the action of viruses and Nd:glass Vulcan drugs on cells can be examined. laser. [3]

Raman laser, uses inelastic Complete 1-2 μm wavelength stimulated coverage; distributed optical Other laser, mostly Raman scattering 1-2 μm for fiber signal amplification for Yb-glass fiber in a nonlinear version telecommunications; optical lasers media, mostly solitons generation and fiber, for amplification amplification

Nuclear pumped See gas lasers Nuclear fission Research laser

APPLICATIONS

Industrial Applications of Laser Today, laser can be found in a broad range of applications within industry, where it can be used for such things as pointing and measuring. In the manufacturing industry, laser is used to measure the ball cylindricity in bearings by observing the dispersion of a laser beam when reflected on the ball. Yet another example is to measure the shadow of a steel band with the help of a laser light to find out the thickness of the band. Within the pulp mill industry the concentration of lye is measured by observing how the laser beam refracts in it. Laser also works as a spirit level and can be used to indicate a flat surface by just sweeping the laser beam along the surface. This is, for instance, used when making walls at building sites. In the mining industry, laser is used to point out the drilling direction.

Laser technologies have also been used within environmental areas. One example is the ability to determine from a distance the environmental toxins in a column of smoke. Other examples are being able to predict and measure the existence of photochemical smog and ozone, both at ground level where it isn't wanted and in the upper layers of the atmosphere where it is needed. Laser is also used to supervise wastewater purification.

Laser works as a light source in all fiber optics in use. It has greater bandwidth (potentially 100,000 times greater) than an ordinary copper cable. It is insensitive to interference from external electrical and magnetic fields. Crosstalk (hearing someone else's phone call) is of rare occurrence. Fiber optics is used increasingly often in data and telecommunications around the world.

Medicine Laser is used in medicine to improve precision work like surgery. Brain surgery is an example of precision surgery that calls for the surgeon to reach the intended area precisely. To make sure of this, lasers are used both to measure and to point in the area in question. Birthmarks, warts and discoloring of the skin can easily be removed with an unfocused laser. The operations are quick and heal quickly and, best of all, they are less painful than ordinary surgery performed with a

scalpel. RECENT APPLICATIONS

DVD A DVD player contains a laser that is used not because it produces a parallel beam, but rather because the light emerges from a tiny point, which enables it to be focused on the different layers of the disc. By moving the lens sideways - laterally, it is possible to reach areas farther in or out on the disc. By moving the lens along the beam - longitudinally, different depths can be reached in the disc. The information, ones and zeros, is stored in several layers, and only one layer is to be read at a time. Every point on a particular layer is read during every revolution of the disc. In order to make room for a lot of information on every disc, the beam has to be focused on as small an area as possible. This cannot be done with any other light source than a laser. Today this area has been reduced to about half a square micrometer, which yields 2 megabits or 0,25 MB(yte) per mm2.

Laser Pointers Laser pointers are made from inexpensive semiconductor lasers that together with a lens produce a parallel beam of light that can be used to make a bright spot to point with. Their range is very large. If one points at a surface 200 meters (220 yards) distant in the dark, a person standing close to the object being pointed at will have no trouble seeing the shining spot (of course, someone else has to hold the laser). On the other hand, the one holding the pointer will have difficulty seeing the spot. The eternal question of range has more to do with the light's behavior on its way back to the sender than with the length of the beam.

Laser Sights Laser sights for rifles and guns can be based on several different principles. Some send a laser beam parallel to the trajectory so that the point of impact becomes visible. This method exposes the marksman. Some project a red dot inside a telescopic sight (instead of cross hairs). In both cases, the dot can be produced with a ring around it.

Speed Measurement Using Laser The method the police use to measure car speed is based on a laser signal that is sent towards the target. This beam bounces back and is mixed with light that has not hit the car. The result is an oscillation - the same as when you tune a guitar - with higher frequency (more treble) the faster the target moves. The speed has to be measured straight from the front or from the back. If it is measured at an angle, the speed is underrated. This means that you cannot get false values that are too high. The measurement is dependent on the car having something that reflects well. The license plate is perfect, as are different types of reflecting objects. Fogged surfaces are okay, but reduce the maximum distance.

Laser Distance Meter The primary users of laser distance meters today are surveyors and constructors, but the car industry is catching on. Least spectacular is the so-called parking assistance that helps the driver to estimate the distance to the car behind when parking. A more recent application measures the distance to the car in front of the driver when driving on highways or other roads. You simply lock in the distance to the car in front of you in order to maintain that distance. This makes driving more efficient and faster as long as it all works. This kind of laser is found in most robots with mechanical vision.

Optical Loudspeaker Cable Any amplifier of worth nowadays has an optical cable for transmission to the loudspeakers. The advantage of this method is that it is insensitive to interference from electromagnetic fields, that is interference from electronic devices and radio transmitters such as cell phones. The light source used as a transmitter is a small laser semiconductor. All equipment using optic cable uses the same standard. For example, the maximum bit rate for broadband applications is today 50- 100 times higher using optics, but the potential ratio is 10,000 times.

RECENT DISCOVERIES 1964

Townes, Basov and Prokhorov shared the prize for their fundamental work, which led to the construction of lasers. They founded the theory of lasers and described how a laser could be built, originating from a similar appliance for microwaves called the MASER that was introduced during the '50s (The MASER has not been used as much as the laser). However, the first functioning laser was not built by them, but by Maiman in 1960.

This was the work that resulted in the big and rather clumsy lasers built in the beginning of the '60s. Still, their theory for the laser effect is the one that fundamentally describes all lasers. Every time you listen to a CD or point with a laser pointer, you hold their discovery in your hand.

1971 Gabor (alone) was given the prize, having founded the basic ideas of the holographic method, which is a famous and spectacular application of laser technology. At first "just" a method of creating 3-D pictures, it has since become a useful tool for the observation of vibrating objects. Much of what we today know about how musical instruments produce their tones is due to the use of holograms. In addition to holograms that can be bought and hung on a wall, simpler holograms can be found on many other things where you might not expect to find them. Small holograms are present on many credit cards and identity cards in order to make them more difficult to forge.

1981 Bloembergen and Schawlow received the prize for their contribution to the development of laser spectroscopy. One typical application of this is nonlinear optics which means methods of influencing one light beam with another and permanently joining several laser beams (not just mixing them - compare the difference between mixing two substances and making them chemically react with one another). These phenomena mean that a light beam can in principle be steered by another light beam. If in the future someone intends to build an optical computer (that could be much faster and much more efficient in storing data), it would have to be based on a nonlinear optic.

When using optical fibers, for example in broadband applications, several of the switches and amplifiers that are used require nonlinear optical effects.

1997 Chu, Cohen-Tannoudji and Phillips et al. received the prize for their developments of methods to cool and trap atoms with laser light which is a method for inducing atoms to relinquish their heat energy to laser light and thus reach lower and lower temperatures. When their temperature sinks very close to absolute zero, atoms form aggregates (make clumps) in a way that reveals some of the innermost aspects of nature. And that is the important application of , namely to make us understand more of nature. Very soon after the discovery other scientists started to use the technique to further develop closely related areas.

2000 Alferov and Kroemer were given the prize for their development within the field of semiconductor physics, where they had studied the type of substances that was first used to build semiconductor lasers, that is, the kind of miniature lasers that today have become the cheapest, lightest and smallest. The idea is to produce both the light source and energy supply and place the mirrors in one crystal (less than 1 mm facet, with many sequences). This has become not only the basis for many cheap and portable appliances, but also the foundation in optical information networks. The CD player, laser writer, laser pointer and the bar code reader the cashier at the supermarket uses, are all based on their discovery.

REFRENCES

*NEWAGE PUBLISHER PVT. LTD.,LASERANDNONLINEAROPTICS,P.B LAUD

*macmillan publisher,laser theory and application,k.dhyacagrajan,ak.ghatak

*universities publishers,laser,e.a siegman

*http://www.nobel.org