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LIST OF CONTENTS

CONTENTS PAGE

CONCEPT OF LASER

HISTORY AND DEVELOPMENT OF

LASER

TYPES OF LASER

WORKING PRINCIPLE OF A LASER

USES OF LASER IN MILITARY

USES OF LASER IN MEDICAL

FIELD

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Laser

Laser Light Concept

Laser light is very different from normallight. Laser light has the following properties:

. It contains one specific wavelength of light (one specific color). The wavelength of

light is determined by the amount of energy released when the electron drops to a

lower orbit.

The light released is coherent. It is organized -- each photon moves in step with the

others. This means that all of the photons have wave fronts that launch in unison.

The light is very directional. A laser light has a very tight beam and is very strong andconcentrated. A flashlight, on the other hand, releases light in many directions, and the

light is very weak and diffuse.

The wavelength (color) of laser light is extremely pure (monochromatic) when compared to

other sources of light, and all of the photons (energy) that make up the laser beam have a

fixed phase relationship (coherence) with respect to one another. Light from a laser typically

has very low divergence. It can travel over great distances or can be focused to a very small

spot with a brightness which exceeds that of the sun. Because of these properties, lasers are

used in a wide variety of applications in all walks of life.

To make these three properties occur takes something called stimulated emission. This doesnot occur in your ordinary flashlight -- in a flashlight, all of the atoms release their photons

randomly. In stimulated emission, photon emission is organized.

The photon that any atom releases has a certain wavelength that is dependent on the energy

difference between the excited state and the ground state. If this photon (possessing a certain

energy and phase) should encounter another atom that has an electron in the same excited

state, stimulated emission can occur. The first photon can stimulate or induce atomic

emission such that the subsequent emitted photon (from the second atom) vibrates with the

same frequency and direction as the incoming photon.

The other key to a laser is a pair of mirrors, one at each end of the lasing medium. Photons,

with a very specific wavelength and phase, reflect off the mirrors to travel back and forththrough the lasing medium. In the process, they stimulate other electrons to make the

downward energy jump and can cause the emission of more photons of the same wavelength

and phase. A cascade effect occurs, and soon we have propagated many, many photons of the

same wavelength and phase. The mirror at one end of the laser is "half-silvered," meaning it

reflects some light and lets some light through. The light that makes it through is the laser

light.

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Gas Laser

The first gas laser (helium neon) was invented by Ali Javan in 1960. The gas laser was thefirst continuous-light laser and the first to operate "on the principle of converting electrical

energy to a laser light output." It has been used in many practical applications.

Robert Hall - Semiconductor Injection Laser

In 1962, Robert Hall created a revolutionary type of laser that is still used in many of the

electronic appliances and communications systems that we use every day.

Kumar Patel - Carbon Dioxide Laser

The carbon dioxide laser was invented by Kumar Patel in 1964.

Hildreth "Hal" Walker - Laser Telemetry

Hildreth Walker invented laser telemetry and targeting systems.

Doctor Steven Trokel patented the Excimer laser for vision correction. The Excimer laser was

originally used for etching silicone computer chips in the 1970s. Working in the IBM

research laboratories in 1982, Rangaswamy Srinivasin,James Wynne, andSamuel

Blumsaw the potential of the Excimer laser in interacting with biological tissue. Srinivasinand the IBM team realized that you could remove tissue with a laser without causing any heat

damage to the neighboring material.

Steven Trokel

New York City ophthalmologist, Steven Trokel made the connection to the cornea and

performed the first laser surgery on a patient's eyes in 1987. The next ten years were spent

perfecting the equipment and the techniques used in laser eye surgery. In 1996, the first

Excimer laser for ophthalmic refractive use was approved in the United States.

Note: It took the observations of Dr. Fyodorov in a case of eye trauma in the 1970's to bring

about the practical application of refractive surgery through radial keratotomy.

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TYPES OF LASERS

Gas laser

Laser gain medium and

type Applications and notes

Helium-neon laserInterferometry,holography, spectroscopy,barcode scanning,

alignment, optical demonstrations.

Argon laserRetinalphototherapy (fordiabetes), lithography, confocal

microscopy, spectroscopy pumping other lasers.

Krypton laserScientific research, mixed withargonto create "white-light" lasers,

light shows.

Xenon ion laser Scientific research.

Nitrogen laser

Pumping of dye lasers, measuring air pollution, scientific research.

Nitrogen lasers can operate superradiantly (without a resonator

cavity). Amateur laser construction. SeeTEA laser

Carbon dioxide laser Material processing (cutting

,welding

, etc.),surgery

.

Carbon monoxide laserMaterial processing (engraving, welding, etc.),photoacoustic

spectroscopy.

Excimer laserUltravioletlithographyforsemiconductor manufacturing,

lasersurgery, LASIK.

Chemical laser

Laser gain medium and typeApplications and notes

Hydrogen fluoride laser

Used in research for laser weaponry by the U.S. DOD, operated

in continuous wave mode, can have power in

the megawattrange.

Deuterium fluoride laserMIRACL,Pulsed Energy Projectile &Tactical High Energy

Laser

COIL(Chemicaloxygen-

iodinelaser)

Laser weaponry, scientific and materials research, laser used in the

U.S. military'sAirborne laser, operated incontinuous

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wavemode, can have power in the megawatt range.

Agil (All gas-phase iodine

laser)Scientific, weaponry, aerospace.

Dye laser

Laser gain medium and typeApplications and notes

Dye lasers

Research, laser medicine,[2]spectroscopy,birthmark removal, isotope separation. The

tuning range of the laser depends on which dye is used.

Metal-vapor laser

Laser gain medium and type Applications

Helium-cadmium (HeCd) metal-vapor laserPrinting and t

paper currenc

Helium-mercury (HeHg) metal-vapor laser Rare, scientifi

Helium-selenium (HeSe) metal-vapor laser Rare, scientifi

Helium-silver (HeAg) metal-vapor laser[3] Scientific rese

Neon-copper (NeCu) metal-vapor laser[3] Dermatologic

Copper vapor laser Rare, dermatological and photodynamic the

Solid-state laser

Laser gain medium

and type

Applications and notes

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Ruby laserHolography,tattoo removal. The first type of visible light laser

invented; May1960.

Nd:YAG laser

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 mostcommon high power lasers. Usually pulsed (down to fractions of

a nanosecond)

Er:YAG laser Periodontal scaling, Dentistry

Neodymium YLF

(Nd:YLF) solid-state

laser

Mostly used for pulsed pumping of certain types of

pulsedTi:sapphire lasers, combined withfrequency doubling.

Neodymium dopedY

ttriumorthovanada

te(Nd:YVO4) laser

Mostly used for continuous pumping ofmode-locked Ti:sapphire

or dye lasers, in combination withfrequency doubling. Also used

pulsed for marking and micromachining. A frequency doubled

nd:YVO4 laser is also the normal way of making agreen laser

pointer.

Neodymium doped

yttrium calcium

oxoborateNd:YCa4O

(BO3)3 or simply

Nd:YCOB

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 forsecond harmonic generation. Such

materials have the potential to simplify the design of high brightness

green lasers.

Neodymium

glass(Nd:Glass) laser

Used in extremely high power (terawatt scale), high energy

(megajoules) multiple beam systems forinertial confinement

fusion. Nd:Glass lasers are usuallyfrequency tripled to the third

harmonic at 351 nm in laser fusion devices.

Semi-conductor laser

Laser gain medium and

type Applications and notes

Semiconductorlaser

diode(general information)

Telecommunications,holography,printing, weapons,

machining, welding, pump sources for other lasers.

GaN Optical discs.

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AlGaInP, AlGaAs

Optical discs, laser pointers, data communications.

780 nmCompact Disc player laser is the most common laser

type in the world. Solid-state laser pumping, machining,

medical.

InGaAsP Telecommunications, solid-state laser pumping, machining,medical..

Vertical cavity surface

emitting laser (VCSEL)Telecommunications

Quantum cascade laser

Research,Future applications may include collision-avoidance

radar, industrial-process control and medical diagnostics such

as breath analyzers.

Other types of laser

Laser gain medium and typeApplications and notes

Free electron laser atmospheric research, material science, medicalapplications.

Gas dynamic laserMilitary applications; can operate in CW mode at

several megawatts optical power.

"Nickel-like" Samariumlaser

First demonstration of efficient "saturated" operation of

a sub10 nm X-ray laser, possible applications in high

resolutionmicroscopy andholography, operation is

close to the water window at 2.2 to 4.4 nm where

observation ofDNA structure and the action

ofviruses and drugs on cells can be examined.

Raman laser, uses inelastic

stimulatedRaman scattering in a

nonlinear media, mostly fiber, for

amplification

Complete 1-2 m wavelength coverage;

distributed optical signal

amplification fortelecommunications;

optical solitons generation and amplification

Nuclear pumped laser Research

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WORKING PRINCIPLE OF A LASER

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 athigher 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).

For a ruby laser, a crystal of ruby is formed into 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 chromium 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.

How lasers work?

Step 1

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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.

Step 2

.

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 amplifiedStep 3

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Mirrors at each end reflect the photons back and forth, continuing this process of stimulated

emission and amplification.

Step 4

The photons leave through the partially silvered mirror at one end. This is laser light

APPLICATIONS OF LASER

ScientificIn science, lasers are used in many ways, including:

A wide variety ofinterferometric techniques

Raman spectroscopy

Laser induced breakdown spectroscopy

Atmospheric remote sensing

Investigating nonlinear optics phenomena

Holographic techniques employing lasers also contribute to a number of

measurement techniques. Laser based LIght Detection And Ranging (LIDAR) technology has application in

geology, seismology, remote sensing andatmospheric physics.

Lasers have been used aboard spacecraft such as in the Cassini-Huygens mission.

In astronomy, lasers have been used to create artificial laser guide stars, used as

reference objects foradaptive optics telescopes.

Lasers may also be indirectly used in spectroscopy as a micro-sampling system, a technique

termed Laserablation (LA), which is typically applied toICP-MSapparatus resulting in the

powerful LA-ICP-MS.

The principles of laser spectroscopy are discussed by Demtrder

[1]

and the use of tunablelasers in spectroscopy are described in Tunable Laser Applications.[2] ).

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Spectroscopy

Most types of laser are an inherently pure source of light; they emit near-monochromatic

light with a very well defined range ofwavelengths. By careful design of the laser

components, the purity of the laser light (measured as the "linewidth") can be improved

more than the purity of any other light source. This makes the laser a very useful source for

spectroscopy. The high intensity of light that can be achieved in a small, well collimated

beam can also be used to induce a nonlinear optical effect in a sample, which makes

techniques such as Raman spectroscopypossible. Other spectroscopic techniques based on

lasers can be used to make extremely sensitive detectors of various molecules, able to

measure molecular concentrations in the parts-per-1012 (ppt) level. Due to the high power

densities achievable by lasers, beam-induced atomic emission is possible: this technique is

termed Laser induced breakdown spectroscopy(LIBS

Lunar laser ranging

When the Apollo astronauts visited the moon, they plantedretroreflector arrays to make

possible the Lunar Laser Ranging Experiment. Laser beams are focused through large

telescopes on Earth aimed toward the arrays, and the time taken for the beam to be reflectedback to Earth measured to determine the distance between the Earth and Moon with high

accuracy.

Material processing

Laser cutting, laser welding, laser brazing, laser bending, laser engraving or marking, laser

cleaning, weapons etc. When the material is exposed to laser it produce intense heat thus the

material is heated and melted.

Photochemistry

Some laser systems, through the process ofmodelocking, can produce extremely brief

pulses of light - as short as picoseconds or femtoseconds (1012 - 1015seconds). Such pulses

can be used to initiate and analyse chemical reactions, a technique known asphotochemistry.The short pulses can be used to probe the process of the reaction at a very high temporal

resolution, allowing the detection of short-lived intermediate molecules. This method is

particularly useful in biochemistry, where it is used to analyse details of protein folding and

function.

Also, it has the binary functions to seal anything it has in the human eye of each atomic

particle in its system.

Laser cooling

A technique that has recent success is laser cooling. This involves atom trapping, a method

where a number of atoms are confined in a specially shaped arrangement ofelectric and

magnetic fields. Shining particular wavelengths of laser light at the ions or atoms slows

them down, thus coolingthem. As this process is continued, they all are slowed and have the

same energy level, forming an unusual arrangement of matter known as a Bose-Einstein

condensate.

Nuclear fusion

Some of the world's most powerful and complex arrangements of multiple lasers and optical

amplifiers are used to produce extremely high intensity pulses of light of extremely short

duration. These pulses are arranged such that they impact pellets oftritium-deuteriumsimultaneously from all directions, hoping that the squeezing effect of the impacts will induce

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atomic fusion in the pellets. This technique, known as "inertial confinement fusion", so

far has not been able to achieve "breakeven", that is, so far the fusion reaction generates less

power than is used to power the lasers, but research continues.

Microscopy

Confocal laser scanning microscopy andTwo-photon excitation microscopy makeuse of lasers to obtain blur-free images of thick specimens at various depths. Laser capture

microdissectionuse lasers to procure specific cell populations from a tissue section under

microscopic visualization.

Additional laser microscopy techniques include harmonic microscopy, four-wave mixing

microscopy and interferometric microscopy.[4]

Military

Military uses of lasers include applications such as target designationand ranging,

defensive countermeasures, communications and directed energy weapons. Directedenergy weapons are also in use, such as BoeingsAirborne Laser which was constructed

inside a Boeing 747. It disrupts the trajectory of shoulder-fired missiles.[5]

On March 18, 2009 Northrop Grumman announced that its engineers in Redondo Beach

had successfully built and tested an electric laser capable of producing a 100-kilowatt ray of

light, powerful enough to destroy cruise missiles, artillery, rockets and mortar rounds.[6] An

electric laser is theoretically capable, according to Brian Strickland, manager for the United

States Army's Joint High Power Solid State Laser program, of being mounted in an aircraft,

ship, or vehicle because it requires much less space for its supporting equipment than a

chemical laser.[7]

On 19 July 2010 an anti-aircraft laser was unveiled at the Farnborough Airshow[2]. It wasdescribed as the LaserClose-In Weapon System.

Defensive countermeasures

Defensive countermeasure applications can range from compact, low power infrared

countermeasures to high power, airborne laser systems. IR countermeasure systems use lasers

to confuse the seeker heads on heat-seeking anti-aircraft missiles. High power boost-phase

intercept laser systems use a complex system of lasers to find, track and destroy

intercontinental ballistic missiles(ICBM). In this type of system achemical laser, one

in which the laser operation is powered by an energetic chemical reaction, is used as the main

weapon beam (seeAirborne Laser). The Mobile Tactical High-Energy Laser (MTHEL)

is another defensive laser system under development; this is envisioned as a field-deployableweapon system able to track incoming artillery projectiles and cruise missiles byradar

and destroy them with a powerful deuterium fluoride laser.

Another example of direct use of a laser as a defensive weapon was researched for the

Strategic Defense Initiative (SDI, nicknamed "Star Wars"), and its successor programs.

This project would use ground-based or space-based laser systems to destroy incoming

intercontinental ballistic missiles(ICBMs). The practical problems of using and aiming

these systems were many; particularly the problem of destroying ICBMs at the most

opportune moment, the boost phase just after launch. This would involve directing a laser

through a large distance in the atmosphere, which, due to optical scattering and

refraction, would bend and distort the laser beam, complicating the aiming of the laser andreducing its efficiency.

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Another idea to come from the SDI project was the nuclear-pumped X-ray laser. This was

essentially an orbiting atomic bomb, surrounded by laser media in the form of glass rods;

when the bomb exploded, the rods would be bombarded with highly-energeticgamma-

rayphotons, causing spontaneous and stimulated emission ofX-ray photons in the

atoms making up the rods. This would lead to optical amplification of the X-ray photons,

producing an X-ray laser beam that would be minimally affected by atmospheric distortionand capable of destroying ICBMs in flight. TheX-ray laserwould be a strictly one-shotdevice, destroying itself on activation. Some initial tests of this concept were performed with

underground nuclear testing; however, the results were not encouraging. Research into

this approach to missile defense was discontinued after the SDI program was cancelled.

Targeting

Target designator

A target designator

Another military use of lasers is as a laser target designator. This is a low-powerlaser

pointer used to indicate a target for aprecision-guided munition, typically launched froman aircraft. The guided munition adjusts its flight-path to home in to the laser light reflected

by the target, enabling a great precision in aiming. The beam of the laser target designator is

set to a pulse rate that matches that set on the guided munition to ensure munitions strike their

designated targets and do not follow other laser beams which may be in use in the area. The

laser designator can be shone onto the target by an aircraft or nearby infantry. Lasers used for

this purpose are usually infrared lasers, so the enemy cannot easily detect the guiding laser

light.

Firearms

Laser sight

Smith & Wesson revolver equipped with a laser sight mounted on the trigger guard.

The laser has in most firearms applications been used as a tool to enhance the targeting of

other weapon systems. For example, a laser sightis a small, usually visible-light laser placed

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on a handgun or a rifle and aligned to emit a beam parallel to the barrel. Since a laser beam

by definition has low divergence, the laser light appears as a small spot even at long

distances; the user places the spot on the desired target and the barrel of the gun is aligned

(but not necessarily allowing forbullet drop,windage and the target moving while the

bullet travels).

Most laser sights use a red laser diode. Others use aninfrared diode to produce a dot

invisible to the naked human eye but detectable with night vision devices. The firearms

adaptive target acquisition moduleLLM01 laser light module combines visible and

infrared laser diodes. In the late 1990s, green diode pumped solid state laser (DPSS)

laser sights (532 nm) became available. Modern laser sights are small and light enough for

attachment to the firearms.

In 2007, LaserMax, a company specializing in manufacturing lasers for military and police

firearms, introduced the first mass-production green laser available for small arms. [8]This

laser mounts to the underside of a handgun or long arm on the accessory rail. The green laser

is supposed to be more visible than the red laser in bright lighting conditions because, for the

same wattage, green light appears brighter than red light.Eye-targeted lasers

A non-lethal laser weapon was developed by the U.S. Air Force to temporarily impair an

adversarys ability to fire a weapon or to otherwise threaten enemy forces. This unit

illuminates an opponent with harmless low-power laser light and can have the effect of

dazzling or disorienting the subject or causing him to flee. Several types ofdazzlers are now

available, and some have been used in combat.

There remains the possibility of using lasers to blind, since this requires much lower power

levels, and is easily achievable in a man-portable unit. However, most nations regard the

deliberate permanent blinding of the enemy as forbidden by the rules of war (see Protocol

on Blinding Laser Weapons). Although several nations have developed blinding laserweapons, such as China'sZM-87, none of these are believed to have made it past the

prototype stage.

In addition to the applications that crossover with military applications, a widely known law

enforcement use of lasers is forlidar to measure the speed of vehicles.

Medical

Cosmetic surgery (removing tattoos, scars, stretch marks, sunspots, wrinkles,

birthmarks, and hairs): see laser hair removal. Laser types used indermatology

include ruby(694 nm), alexandrite (755 nm), pulsed diode array (810 nm),

Nd:YAG (1064 nm),Ho:YAG (2090 nm), and Er:YAG (2940 nm). Eye surgery and refractive surgery

Soft tissue surgery:CO2,Er:YAG laser

Laser scalpel (General surgery, gynecological, urology, laparoscopic)

Photobiomodulation (i.e. laser therapy)

"No-Touch" removal of tumors, especially of the brain and spinal cord.

In dentistryforcaries removal,endodontic/periodontic procedures, tooth

whitening, andoral surgery

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Industrial and commercial

Lasers used for visual effects during a musical performance. (Alaser light show.)

Levelling of ceramic tiles floor with a laser device

Cutting and peeningof metals and other material, welding, marking, etc.

Guidance systems (e.g.,ring laser gyroscopes)

Rangefinder /surveying,

LIDAR / pollution monitoring,

Digital minilabs

Barcode readers

Laser engraving of printing plate

Laser bonding of additive marking materials for decoration and identification,

Laser pointers

Laser accelerometers

Holography

Bubblegrams

Photolithography

Optical communications (overoptical fiberor infree space)

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Optical tweezers

Writing subtitles onto motion picturefilms.[9]

Space elevator, a possible solution transfer energy to the climbers by laser ormicrowavepower beaming

3D laser scanners for accurate 3D measurement.

Laser line levels are used in surveying and construction. Lasers are also used for

guidance for aircraft.

Extensively in both consumer and industrial imaging equipment.

In laser printers: gas and diode lasers play a key role in manufacturing high

resolution printing plates and in image scanning equipment.

Diode lasers are used as a lightswitch in industry, with a laser beam and a receiver

which will switch on or off when the beam is interrupted, and because a laser can

keep the light intensity over larger distances than a normal light, and is more precise

than a normal light it can be used for product detection in automated production. Laser alignment

Additive manufacturing

In consumer electronics, telecommunications, and data communications, lasers are

used as the transmitters in optical communications overoptical fiber and free space.

To store and retrieve data in optical discs

Laser lighting displays (pictured) accompany many music concerts.