TERM PAPER

LASER, ACTION, EINSTEIN THEORY OF LASER, 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 lasers

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 infrared 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 ruby laser, 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 storedLight 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 gain medium

and type  

Operation wavelength(s)

Pump source Applications and notes

Helium-neon laser

632.8 nm (543.5 nm, 593.9 nm, 611.8 nm, 1.1523 μm, 1.52 μm, 3.3913 μm)

Electrical discharge

Interferometry, holography, spectroscopy, barcode scanning, alignment, optical demonstrations.

Argon laser

454.6 nm, 488.0 nm, 514.5 nm (351 nm, 363.8, 457.9 nm, 465.8 nm, 476.5 nm, 472.7 nm, 528.7 nm, also frequency doubled to provide 244 nm, 257 nm)

Electrical discharge

Retinal phototherapy (for diabetes), lithography, confocal microscopy,spectroscopy pumping other lasers.

Krypton laser

416 nm, 530.9 nm, 568.2 nm, 647.1 nm, 676.4 nm, 752.5 nm, 799.3 nm

Electrical discharge

Scientific research, mixed with argon to create "white-light" lasers, light shows.

Xenon ion laser

Many lines throughout visible spectrum extending into the UV and IR.

Electrical discharge

Scientific research.

Nitrogen laser

337.1 nmElectrical discharge

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

Carbon dioxide laser

10.6 μm, (9.4 μm)

Transverse (high power) or longitudinal (low power) electrical discharge

Material processing (cutting, welding, etc.), surgery.

Carbon monoxide laser

2.6 to 4 μm, 4.8 to 8.3 μm

Electrical discharge

Material processing (engraving, welding, etc.), photoacoustic spectroscopy.

Excimer laser

193 nm (ArF), 248 nm (KrF), 308 nm (XeCl), 353 nm (XeF)

Excimer recombination via electrical discharge

Ultraviolet lithography for semiconductor manufacturing, laser surgery, LASIK.

CHEMICAL LASERS

Chemical laser

Used as directed-energy weapons.

Laser gain Operation Pump source Applications and notes

medium and type  

wavelength(s)

Hydrogen fluoride laser

2.7 to 2.9 μm for Hydrogen fluoride (<80% Atmospheric transmittance)

Chemical reaction in a burning jet of ethylene and nitrogen trifluoride (NF3)

Used in research for laser weaponry by the U.S. DOD, operated in continuous wave mode, can have power in the megawatt range.

Deuterium fluoride laser

~3800 nm (3.6 to 4.2 μm) (~90% Atm. transmittance)

chemical reactionMIRACL, Pulsed Energy Projectile & Tactical High Energy Laser

COIL (Chemical oxygen-iodine laser)

1.315 μm (<70% Atmospheric transmittance)

Chemical reaction in a jet of singlet delta oxygen and iodine

Laser weaponry, scientific and materials research, laser used in the U.S. military's Airborne laser, operated in continuous wave mode, can have power in the megawatt range.

Agil (All gas-phase iodine laser)

1.315 μm (<70% Atmospheric transmittance)

Chemical reaction of chlorine atoms with gaseous hydrazoic acid, resulting in excited molecules of nitrogen chloride, which then pass their energy to the iodine atoms.

Scientific, weaponry, aerospace.

DYE LASER

Dye laser

Laser gain medium

and type  Operation wavelength(s)

Pump source

Applications and notes

Dye lasers 390-435 nm (stilbene), 460-515 nm (coumarin 102), 570-640 nm (rhodamine 6G),

Other laser, flashlamp

Research, spectroscopy, birthmark removal, isotope separation. The tuning range of

many othersthe laser depends on which dye is used.

METAL-VAPOR LASERS

Laser gain medium and

type  

Operation wavelength(s)

Pump source Applications and notes

Helium-cadmium (HeCd) metal-vapor laser

441.563 nm, 325 nm

Electrical discharge in metal vapor mixed with helium buffer gas.

Printing and typesetting applications, fluorescence excitation examination (ie. in U.S. paper currency printing), scientific research.

Helium-mercury (HeHg) metal-vapor laser

567 nm, 615 nmRare, scientific research, amateur laser construction.

Helium-selenium (HeSe) metal-vapor laser

up to 24 wavelengths between red and UV

Rare, scientific research, amateur laser construction.

Helium-silver (HeAg) metal-vapor laser

224.3 Scientific research

Neon-copper (NeCu) metal-vapor laser

248.6

Electrical discharge in metal vapor mixed with neon buffer gas.

Scientific research

Copper vapor laser

510.6 nm, 578.2 nm

Electrical discharge

Dermatological uses, high speed photography, pump for dye lasers.

Gold vapor laser

627 nmRare, dermatological and photodynamic therapy uses.

SOLID-STATE LASER

Laser gain medium and type  

Operation wavelength(s)

Pump source Applications and notes

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

Nd:YAG laser1.064 μm, (1.32 μm)

Flashlamp, laser diode

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

Er:YAG laser 2.94 μmFlashlamp, laser diode

Periodontal scaling, Dentistry

Neodymium YLF (Nd:YLF) solid-state laser

1.047 and 1.053 μm

Flashlamp, laser diode

Mostly used for pulsed pumping of certain types of pulsed Ti:sapphire lasers, combined with frequency doubling.

Neodymium doped Yttrium orthovanadate (Nd:YVO4) laser

1.064 μm laser diode Mostly used for continuous pumping of mode-locked Ti:sapphire or dye lasers, in 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 laser pointer.

Neodymium doped yttrium calcium oxoborate Nd:Y Ca 4O(BO3)3 or simply Nd:YCOB

~1.060 μm (~530 nm at second harmonic)

laser diode

Nd:YCOB is a so called "self-frequency doubling" or SFD laser material which is both capable of lasing and which has nonlinear characteristics suitable for second harmonic generation. Such materials have the potential to simplify the design of high brightness green lasers.

Neodymium glass (Nd:Glass) laser

~1.062 μm (Silicate glasses), ~1.054 μm (Phosphate glasses)

Flashlamp, laser diode

Used in extremely high power (terawatt scale), high energy (megajoules) multiple beam systems for inertial confinement fusion. Nd:Glass lasers are usually frequency tripled to the third harmonic at 351 nm in laser fusion devices.

Titanium sapphire (Ti:sapphire) laser

650-1100 nm Other laser

Spectroscopy, LIDAR, research. This material is often used in highly-tunable mode-locked infrared lasers to produce ultrashort pulses and in amplifier lasers to produce ultrashort and ultra-intense pulses.

Thulium YAG (Tm:YAG) laser

2.0 μm Laser diode LIDAR.

Ytterbium YAG (Yb:YAG) laser

1.03 μmLaser diode, flashlamp

Optical refrigeration, materials processing, ultrashort pulse research, multiphoton microscopy, LIDAR.

Ytterbium:2O3 (glass or ceramics) laser

1.03 μm Laser diode ultrashort pulse research, [3]

Ytterbium doped glass laser (rod, plate/chip, and fiber)

1. μm Laser diode.

Fiber version is capable of producing several-kilowatt continuous power, having ~70-80% optical-to-optical and ~25% electrical-to-optical efficiency. Material processing: cutting, welding, marking; nonlinear fiber optics: broadband fiber-nonlinearity based sources, pump for fiber Raman lasers; distributed Raman amplification pump for telecommunications.

Holmium YAG (Ho:YAG) laser

2.1 μm Laser diodeTissue ablation, kidney stone removal, dentistry.

Cerium doped lithium strontium(or calcium) aluminum fluoride (Ce:LiSAF, Ce:LiCAF)

~280 to 316 nm

Frequency quadrupled Nd:YAG laser pumped, excimer laser pumped, copper vapor laser pumped.

Remote atmospheric sensing, LIDAR, optics research.

Promethium 147 doped phosphate glass (147Pm+3:Glass) solid-state laser

933 nm, 1098 nm

 ??

Laser material is radioactive. Once demonstrated in use at LLNL in 1987, room temperature 4 level lasing in 147Pm doped into a lead-indium-phosphate glass étalon.

Chromium doped chrysoberyl (alexandrite) laser

Typically tuned in the range of 700 to 820 nm

Flashlamp, laser diode, mercury arc (for CW mode operation)

Dermatological uses, LIDAR, laser machining.

Erbium doped and erbium-ytterbium codoped glass lasers

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

telecommunications.

Trivalent uranium doped calcium fluoride (U:CaF2) solid-state laser

2.5 μm Flashlamp

First 4-level solid state laser (November 1960) developed by Peter Sorokin and Mirek Stevenson at IBM research labs, second laser invented overall (after Maiman's ruby laser), liquid helium cooled, unused today. [1]

Divalent samarium doped calcium fluoride (Sm:CaF2) laser

708.5 nm Flashlamp

Also invented by Peter Sorokin and Mirek Stevenson at IBM research labs, early 1961. Liquid helium cooled, unused today. [2]

F-center laser. 2.3-3.3 μm Ion laser Spectroscopy

SEMICONDUCTOR LASER

Laser diode

Laser gain medium and

type  

Operation wavelength(s)

Pump source

Applications and notes

Semiconductor laser diode (general information)

0.4-20 μm, depending on active region material.

Electrical current

Telecommunications, holography, printing, weapons, machining, welding, pump sources for other lasers.

GaN 0.4 μm Optical discs.

AlGaAs 0.63-0.9 μm Optical discs, laser pointers, data communications. 780 nm Compact Disc player laser is the most common laser type in the world. Solid-state laser pumping, machining, medical.

InGaAsP 1.0-2.1 μmTelecommunications, solid-state laser pumping, machining, medical..

lead salt 3-20 μm

Vertical cavity surface emitting laser (VCSEL)

850 - 1500 nm, depending on material

Telecommunications

Quantum cascade laser

Mid-infrared to far-infrared.

Research,Future applications may include collision-avoidance radar, industrial-process control and medical diagnostics such as breath analyzers.

Hybrid silicon laser

Mid-infrared Research

OTHER TYPES OF LASERS

Laser gain medium and

type  

Operation wavelength(s)

Pump source Applications and notes

Free electron laser

A broad wavelength range (about 100 nm - several mm); one free electron laser may be tunable over a wavelength range

relativistic electron beam

atmospheric research, material science, medical applications.

Gas dynamic laser

Several lines around 10.5 um; other frequencies may be possible with different gas mixtures

Spin state population inversion in carbon dioxide molecules caused by supersonic

Military applications; can operate in CW mode at several megawatts optical power.

adiabatic expansion of mixture of nitrogen and carbon dioxide

"Nickel-like" Samarium laser

X-rays at 7.3 nm wavelength

Lasing in ultra-hot samarium plasma formed by double pulse terawatt scale irradiation fluences created by Rutherford Appleton Laboratory's Nd:glass Vulcan laser. [3]

First demonstration of efficient "saturated" operation of a sub–10 nm X-ray laser, possible applications in high resolution microscopy and holography, operation is close to the "water window" at 2.2 to 4.4 nm where observation of DNA structure and the action of viruses and drugs on cells can be examined.

Raman laser, uses inelastic stimulated Raman scattering in a nonlinear media, mostly fiber, for amplification

1-2 μm for fiber version

Other laser, mostly Yb-glass fiber lasers

Complete 1-2 μm wavelength coverage; distributed optical signal amplification for telecommunications; optical solitons generation and amplification

Nuclear pumped laser

See gas lasers Nuclear fission Research

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 laser cooling, 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