termpaper laser physics

7/30/2019 Termpaper Laser Physics

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LOVELY PROFESSI ONAL UNIVERSITY

PHAGWARA(PB.)

SUB : - Mechanics (PHY-101)

Topic: - LASER


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ACKNOWLEDGEMENT

I would like to express my gratitude to all those who gave me the possibility

to complete this term paper. I want to thank the Department of civil

engineering of lovely professional university for giving me permission tocommence this term paper in the first instance, to do the necessary research

work and to use experimental data from different sources. I have

furthermore to thank the HOD. And My class teacher Mrs. ruchika

dhawann, and whole civil engineering department who gave and confirmed

this permission and encouraged me to go ahead with my term paper. I am

bound to the friends, classmates, roommates and my belongings their

stimulating support.

I am deeply indebted to my class teacher Mrs. Ruchika dhawan whose help,stimulating suggestions and encouragement helped me in all the time of

research for and framing of this term paper.

My former colleagues from Delhi University supported me in my research

work. I want to thank them for all their help, support, interest and valuable

hints. Especially I am obliged to Mr Aman Pal Verma, Muninder

singh,sanjeev gautum . I also want to thank library department for all their

assistance on the library computer. My room mates rahul, animehs was of

great help in difficult times. My roommate and friends looked closely at the

final version of the term paper for English style and grammar, correcting

both and offering suggestions for improvement.

Especially, I would like to give my special thanks to my mother,father and

the whole family along with friends whose patient love enabled me to

complete this work.

Thank you again,

- NAVJEET SINGH


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INTRODUCTION

What is laser?

A laser is a device that emits light (electromagnetic radiation) through

a process called stimulated emission. Laser light is usually spatiallycoherent, which means that the light either is emitted in a narrow,low-divergence beam, or can be converted into one with the help ofoptical components such as lenses. More generally, coherent lighttypically means the source produces light waves that are in step.They have the same frequencies and identical phase. The coherenceof typical laser emission is a distinctive characteristic of lasers. Mostother light sources emit incoherent light, which has a phase thatvaries randomly with time and position. Typically, lasers are thought

of as emitting light with a narrow wavelength spectrum("monochromatic" light). This is not true of all lasers, however: someemit light with a broad spectrum, while others emit light at multipledistinct wavelengths simultaneously.

The word laser originated as an acronym for Light Amplification byStimulated Emission of Radiation. The word light in this phrase isused in the broader sense, referring to electromagnetic radiation ofany frequency, not just that in the visible spectrum. Hence there areinfrared lasers, ultraviolet lasers, X-ray lasers, etc. Because the

microwave equivalent of the laser, the maser, was developed first,devices that emit microwave and radio frequencies are usually calledmasers. In early literature, particularly from researchers at BellTelephone Laboratories, the laser was often called the optical maser.This usage has since become uncommon, and as of 1998 even BellLabs uses the term laser.

The back-formed verb to laser means "to produce laser light" or "to

apply laser light to. The word "laser" is sometimes used to describe

other non-light technologies. For example, a source of atoms in a

coherent state is called an "atom laser."
http://wiki/Lighthttp://wiki/Electromagnetic_radiationhttp://wiki/Stimulated_emissionhttp://wiki/Coherence_(physics)http://wiki/Beam_divergencehttp://wiki/Lenshttp://wiki/Phase_(waves)http://wiki/Wavelengthhttp://wiki/Electromagnetic_spectrumhttp://wiki/Acronymhttp://wiki/Electromagnetic_radiationhttp://wiki/Visible_spectrumhttp://wiki/Infraredhttp://wiki/Ultraviolethttp://wiki/X-rayhttp://wiki/Microwavehttp://wiki/Maserhttp://wiki/Radio_frequencyhttp://wiki/Bell_Telephone_Laboratorieshttp://wiki/Bell_Telephone_Laboratorieshttp://wiki/Back-formationhttp://wiki/Atom_laserhttp://wiki/Atom_laserhttp://wiki/Back-formationhttp://wiki/Bell_Telephone_Laboratorieshttp://wiki/Bell_Telephone_Laboratorieshttp://wiki/Bell_Telephone_Laboratorieshttp://wiki/Radio_frequencyhttp://wiki/Maserhttp://wiki/Microwavehttp://wiki/X-rayhttp://wiki/Ultraviolethttp://wiki/Infraredhttp://wiki/Visible_spectrumhttp://wiki/Electromagnetic_radiationhttp://wiki/Acronymhttp://wiki/Electromagnetic_spectrumhttp://wiki/Wavelengthhttp://wiki/Phase_(waves)http://wiki/Lenshttp://wiki/Beam_divergencehttp://wiki/Coherence_(physics)http://wiki/Stimulated_emissionhttp://wiki/Electromagnetic_radiationhttp://wiki/Light


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HISTORY

In 1917 Albert Einstein, in his paper Zur Quantentheorie derStrahlung (On the Quantum Theory of Radiation), laid the foundation

for the invention of the laser and its predecessor, the maser, in aground-breaking rederivation ofMax Planck's law of radiation basedon the concepts of probability coefficients (later to be termed 'Einsteincoefficients') for the absorption, spontaneous emission, andstimulated emission of electromagnetic radiation.

In 1928, Rudolf W. Ladenburg confirmed the existence ofstimulated emission and negative absorption. In 1939, Valentin A.Fabrikant predicted the use of stimulated emission to amplify "short"waves.

In 1947, Willis E. Lamb and R. C. Retherford found apparentstimulated emission in hydrogen spectra and made the firstdemonstration of stimulated emission.

In 1950, Alfred Kastler(Nobel Prize for Physics 1966) proposed themethod of optical pumping, which was experimentally confirmed byBrossel, Kastler and Winter two years later.

On 16 May 1960 The first working laser was demonstrated by

Theodore Maiman at Hughes Research Laboratories. Since then,lasers have become a multi-billion dollar industry. By far the largestsingle application of lasers is in optical storage devices such ascompact disc and DVD players, in which a semiconductor laserlessthan a millimeter wide scans the surface of the disc. The second-largest application is fiber-optic communication. Other commonapplications of lasers are bar code readers, laser printers and laserpointers.
http://wiki/Albert_Einsteinhttp://wiki/Maserhttp://wiki/Max_Planckhttp://wiki/Einstein_coefficientshttp://wiki/Einstein_coefficientshttp://wiki/Rudolf_W._Ladenburghttp://wiki/Willis_E._Lambhttp://wiki/Alfred_Kastlerhttp://wiki/Theodore_Maimanhttp://wiki/Hughes_Research_Laboratorieshttp://wiki/Optical_storagehttp://wiki/Compact_Disc_playerhttp://wiki/DVD_playerhttp://wiki/Semiconductor_laserhttp://wiki/Fiber-optic_communicationhttp://wiki/Bar_codehttp://wiki/Laser_printershttp://wiki/Laser_pointerhttp://wiki/Laser_pointerhttp://wiki/Laser_pointerhttp://wiki/Laser_pointerhttp://wiki/Laser_pointerhttp://wiki/Laser_printershttp://wiki/Bar_codehttp://wiki/Fiber-optic_communicationhttp://wiki/Semiconductor_laserhttp://wiki/DVD_playerhttp://wiki/Compact_Disc_playerhttp://wiki/Optical_storagehttp://wiki/Hughes_Research_Laboratorieshttp://wiki/Theodore_Maimanhttp://wiki/Alfred_Kastlerhttp://wiki/Willis_E._Lambhttp://wiki/Rudolf_W._Ladenburghttp://wiki/Einstein_coefficientshttp://wiki/Einstein_coefficientshttp://wiki/Einstein_coefficientshttp://wiki/Max_Planckhttp://wiki/Maserhttp://wiki/Albert_Einstein


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DESIGN

A laser consists of a gain medium inside a highly reflective opticalcavity, as well as a means to supply energy to the gain medium. Thegain medium is a material with properties that allow it to amplify lightby stimulated emission. In its simplest form, a cavity consists of twomirrors arranged such that light bounces back and forth, each timepassing through the gain medium. Typically one of the two mirrors,

the output coupler, is partially transparent. The output laser beam isemitted through this mirror.

Light of a specific wavelength that passes through the gain medium isamplified (increases in power); the surrounding mirrors ensure thatmost of the light makes many passes through the gain medium, beingamplified repeatedly. Part of the light that is between the mirrors (thatis, within the cavity) passes through the partially transparent mirrorand escapes as a beam of light.

1. Gain medium

2. Laser pumping energy

3. High reflector

4. . Output coupler

5. . Laser beam
http://wiki/Active_laser_mediumhttp://wiki/Optical_cavityhttp://wiki/Optical_cavityhttp://wiki/Output_couplerhttp://wiki/Optical_amplifierhttp://wiki/Light_beamhttp://wiki/Output_couplerhttp://wiki/Output_couplerhttp://wiki/Light_beamhttp://wiki/Optical_amplifierhttp://wiki/Output_couplerhttp://wiki/Optical_cavityhttp://wiki/Optical_cavityhttp://wiki/Optical_cavityhttp://wiki/Active_laser_medium


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LASER PHYSICS

The gain medium of a laser is a material of controlled purity, size,concentration, and shape, which amplifies the beam by the process

of stimulated emission. It can be of any state: gas, liquid, solid orplasma. The gain medium absorbs pump energy, which raises someelectrons into higher-energy ("excited") quantum states. Particles caninteract with light both by absorbing photons and by emitting photons.Emission can be spontaneous or stimulated. In the latter case, thephoton is emitted in the same direction as the light that is passing by.When the number of particles in one excited state exceeds thenumber of particles in some lower-energy state, population inversionis achieved and the amount of stimulated emission due to light that

passes through is larger than the amount of absorption. Hence, thelight is amplified. By itself, this makes an optical amplifier. When anoptical amplifier is placed inside a resonant optical cavity, one obtainsa laser.

The optical cavity, a type ofcavity resonator, contains a coherentbeam of light between reflective surfaces so that the light passesthrough the gain medium more than once before it is emitted from theoutput aperture or lost to diffraction or absorption. As light circulatesthrough the cavity, passing through the gain medium, if the gain

(amplification) in the medium is stronger than the resonator losses,the power of the circulating light can rise exponentially. But eachstimulated emission event returns a particle from its excited state tothe ground state, reducing the capacity of the gain medium for furtheramplification. When this effect becomes strong, the gain is said to besaturated. The balance of pump power against gain saturation andcavity losses produces an equilibrium value of the laser power insidethe cavity; this equilibrium determines the operating point of the laser.If the chosen pump power is too small, the gain is not sufficient toovercome the resonator losses, and the laser will emit only very small

light powers. The minimum pump power needed to begin laser actionis called the lasing threshold. The gain medium will amplify anyphotons passing through it, regardless of direction; but only thephotons aligned with the cavity manage to pass more than oncethrough the medium and so have significant amplification.
http://wiki/State_of_matterhttp://wiki/Gashttp://wiki/Liquidhttp://wiki/Solidhttp://wiki/Plasma_(physics)http://wiki/Excited_statehttp://wiki/Quantum_statehttp://wiki/Population_inversionhttp://wiki/Optical_amplifierhttp://wiki/Cavity_resonatorhttp://wiki/Exponential_growthhttp://wiki/Lasing_thresholdhttp://wiki/Lasing_thresholdhttp://wiki/Exponential_growthhttp://wiki/Cavity_resonatorhttp://wiki/Optical_amplifierhttp://wiki/Population_inversionhttp://wiki/Quantum_statehttp://wiki/Excited_statehttp://wiki/Plasma_(physics)http://wiki/Solidhttp://wiki/Liquidhttp://wiki/Gashttp://wiki/State_of_matter


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The beam in the cavity and the output beam of the laser, if they occurin free space rather than waveguides (as in an optical fiberlaser),are, at best, low orderGaussian beams. However this is rarely thecase with powerful lasers. If the beam is not a low-order Gaussianshape, the transverse modes of the beam can be described as asuperposition ofHermite-Gaussian orLaguerre-Gaussian beams (forstable-cavity lasers). Unstable laser resonators on the other hand,have been shown to produce fractal shaped beams. The beam maybe highly collimated, that is being parallel without diverging. However,a perfectly collimated beam cannot be created, due to diffraction. Thebeam remains collimated over a distance which varies with thesquare of the beam diameter, and eventually diverges at an anglewhich varies inversely with the beam diameter. Thus, a beamgenerated by a small laboratory laser such as a helium-neon laser

spreads to about 1.6 kilometers (1 mile) diameter if shone from theEarth to the Moon. By comparison, the output of a typicalsemiconductor laser, due to its small diameter, diverges almost assoon as it leaves the aperture, at an angle of anything up to 50.However, such a divergent beam can be transformed into acollimated beam by means of a lens. In contrast, the light from non-laser light sources cannot be collimated by optics as well.

Although the laser phenomenon was discovered with the help ofquantum physics, it is not essentially more quantum mechanical than

other light sources. The operation of a free electron lasercan beexplained without reference to quantum mechanics.
http://wiki/Optical_fiberhttp://wiki/Gaussian_beamhttp://wiki/Transverse_modehttp://wiki/Hermite_polynomialshttp://wiki/Gaussian_functionhttp://wiki/Laguerre_polynomialshttp://wiki/Collimated_lighthttp://wiki/Beam_divergencehttp://wiki/Diffractionhttp://wiki/Helium-neon_laserhttp://wiki/Earthhttp://wiki/Moonhttp://wiki/Lens_(optics)http://wiki/Quantum_physicshttp://wiki/Free_electron_laserhttp://wiki/Quantum_mechanicshttp://wiki/Quantum_mechanicshttp://wiki/Free_electron_laserhttp://wiki/Quantum_physicshttp://wiki/Lens_(optics)http://wiki/Moonhttp://wiki/Earthhttp://wiki/Helium-neon_laserhttp://wiki/Diffractionhttp://wiki/Beam_divergencehttp://wiki/Collimated_lighthttp://wiki/Laguerre_polynomialshttp://wiki/Gaussian_functionhttp://wiki/Hermite_polynomialshttp://wiki/Transverse_modehttp://wiki/Gaussian_beamhttp://wiki/Optical_fiber


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OPERATIONS

The output of a laser may be a continuous constant-amplitude output(known as CW orcontinuous wave); or pulsed, by using thetechniques ofQ-switching, mode locking, orgain-switching. In pulsedoperation, much higher peak powers can be achieved.

Some types of lasers, such as dye lasers and vibronic solid-statelasers can produce light over a broad range of wavelengths; thisproperty makes them suitable for generating extremely short pulsesof light, on the order of a few fem to seconds (10-15 s).

Continuous wave operation

In the continuous wave (CW) mode of operation, the output of a laseris relatively constant with respect to time. The population inversionrequired for lasing is continually maintained by a steady pump source.

Pulsed operation

In the pulsed mode of operation, the output of a laser varies withrespect to time, typically taking the form of alternating 'on' and 'off'periods. In many applications one aims to deposit as much energy as

possible at a given place in as short time as possible. In laserablation for example, a small volume of material at the surface of awork piece might evaporate if it gets the energy required to heat it upfar enough in very short time. If, however, the same energy is spreadover a longer time, the heat may have time to disperse into the bulkof the piece, and less material evaporates. There are a number ofmethods to achieve this.

Q-switching

In a Q-switched laser, the population inversion (usually produced inthe same way as CW operation) is allowed to build up by making thecavity conditions (the 'Q') unfavorable for lasing. Then, when thepump energy stored in the laser medium is at the desired level, the'Q' is adjusted (electro- or acousto-optically) to favourable conditions,releasing the pulse. This results in high peak powers as the average
http://wiki/Continuous_wavehttp://wiki/Q-switchinghttp://wiki/Modelockinghttp://wiki/Gain-switchinghttp://wiki/Femtosecondshttp://wiki/Continuous_wavehttp://wiki/Laser_ablationhttp://wiki/Laser_ablationhttp://wiki/Dispersehttp://wiki/Dispersehttp://wiki/Laser_ablationhttp://wiki/Laser_ablationhttp://wiki/Laser_ablationhttp://wiki/Continuous_wavehttp://wiki/Femtosecondshttp://wiki/Gain-switchinghttp://wiki/Modelockinghttp://wiki/Q-switchinghttp://wiki/Continuous_wave


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power of the laser (were it running in CW mode) is packed into ashorter time frame.

ModelockingA mode locked laser emits extremely short pulses on the order oftens ofpicoseconds down to less than 10 fem to seconds. Thesepulses are typically separated by the time that a pulse takes tocomplete one round trip in the resonator cavity. Due to the Fourierlimit (also known as energy-time uncertainty), a pulse of such shorttemporal length has a spectrum which contains a wide range ofwavelengths. Because of this, the laser medium must have a broadenough gain profile to amplify them all. An example of a suitable

material is titanium-doped, artificially grown sapphire (Ti:sapphire).

Pulsed pumping

Another method of achieving pulsed laser operation is to pump thelaser material with a source that is itself pulsed, either throughelectronic charging in the case of flash lamps, or another laser whichis already pulsed. Pulsed pumping was historically used with dyelasers where the inverted population lifetime of a dye molecule wasso short that a high energy, fast pump was needed. The way toovercome this problem was to charge up large capacitors which are

then switched to discharge through flash lamps, producing a broadspectrum pump flash. Pulsed pumping is also required for laserswhich disrupt the gain medium so much during the laser process thatlasing has to cease for a short period. These lasers, such as theexcimer laser and the copper vapor laser, can never be operated inCW mode.
http://wiki/Picosecondhttp://wiki/Femtosecondshttp://wiki/Fourier_transform%23Localization_propertyhttp://wiki/Fourier_transform%23Localization_propertyhttp://wiki/Uncertainty_principlehttp://wiki/Titaniumhttp://wiki/Sapphirehttp://wiki/Ti-sapphire_laserhttp://wiki/Capacitorshttp://wiki/Capacitorshttp://wiki/Ti-sapphire_laserhttp://wiki/Sapphirehttp://wiki/Titaniumhttp://wiki/Uncertainty_principlehttp://wiki/Fourier_transform%23Localization_propertyhttp://wiki/Fourier_transform%23Localization_propertyhttp://wiki/Fourier_transform%23Localization_propertyhttp://wiki/Femtosecondshttp://wiki/Picosecond


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TYPES

GAS LASERSGas lasers using many gases have been built and used for manypurposes.The helium-neon laser(HeNe) emits at a variety ofwavelengths and units operating at 633 nm are very common ineducation because of its low cost.Carbon dioxide lasers can emithundreds of kilowatts at 9.6 m and 10.6 m, and are often used inindustry for cutting and welding. The efficiency of a CO2 laser is over10%.Argon-ion lasers emit light in the range 351-528.7 nm.Depending on the optics and the laser tube a different number of

lines is usable but the most commonly used lines are 458 nm,488 nm and 514.5 nm.A nitrogen transverse electrical discharge ingas at atmospheric pressure (TEA) laser is an inexpensive gas laserproducing UV Light at 337.1 nm.

CHEMICAL LASERS

Chemical lasers are powered by a chemical reaction, and can

achieve high powers in continuous operation. For example, in theHydrogen fluoride laser(2700-2900 nm) and the Deuterium fluoridelaser(3800 nm) the reaction is the combination of hydrogen ordeuterium gas with combustion products ofethylene in nitrogentrifluoride. They were invented by George C. Pimentel.

EXCIMER LASER

Excimer lasers are powered by a chemical reaction involving anexcited dimer, orexcimer, which is a short-lived dimeric or

heterodimeric molecule formed from two species (atoms), at leastone of which is in an excited electronic state. They typically produceultraviolet light, and are used in semiconductorphotolithography andin LASIK eye surgery. Commonly used excimer molecules include F2(fluorine, emitting at 157 nm), and noble gas compounds (ArF[193 nm], KrCl [222 nm], KrF [248 nm], XeCl [308 nm], and XeF[351 nm]).
http://wiki/Gas_laserhttp://wiki/Gashttp://wiki/Helium-neon_laserhttp://wiki/Carbon_dioxide_laserhttp://wiki/%CE%9Cmhttp://wiki/Ion_laserhttp://wiki/TEA_laserhttp://wiki/TEA_laserhttp://wiki/Chemical_laserhttp://wiki/Hydrogen_fluoride_laserhttp://wiki/Deuterium_fluoride_laserhttp://wiki/Deuterium_fluoride_laserhttp://wiki/Ethylenehttp://wiki/Nitrogen_trifluoridehttp://wiki/Nitrogen_trifluoridehttp://wiki/George_C._Pimentelhttp://wiki/Excimer_laserhttp://wiki/Excimerhttp://wiki/Excited_statehttp://wiki/Ultraviolethttp://wiki/Photolithographyhttp://wiki/LASIKhttp://wiki/Fluorinehttp://wiki/Category:Noble_gas_compoundshttp://wiki/Category:Noble_gas_compoundshttp://wiki/Fluorinehttp://wiki/LASIKhttp://wiki/Photolithographyhttp://wiki/Ultraviolethttp://wiki/Excited_statehttp://wiki/Excimerhttp://wiki/Excimer_laserhttp://wiki/George_C._Pimentelhttp://wiki/Nitrogen_trifluoridehttp://wiki/Nitrogen_trifluoridehttp://wiki/Nitrogen_trifluoridehttp://wiki/Ethylenehttp://wiki/Deuterium_fluoride_laserhttp://wiki/Deuterium_fluoride_laserhttp://wiki/Deuterium_fluoride_laserhttp://wiki/Hydrogen_fluoride_laserhttp://wiki/Chemical_laserhttp://wiki/TEA_laserhttp://wiki/TEA_laserhttp://wiki/Ion_laserhttp://wiki/%CE%9Cmhttp://wiki/Carbon_dioxide_laserhttp://wiki/Helium-neon_laserhttp://wiki/Gashttp://wiki/Gas_laser


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SOLID-STATE LASERS

Solid-state lasermaterials are commonly made by "doping" acrystalline solid host 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 actuallymaintained in the "dopant", such as chromium orneodymium.Formally, the class of solid-state lasers includes also fiber laser, asthe active medium (fiber) is in the solid state. Practically, in thescientific literature, solid-state laserusually means a laser with bulkactive medium, while wave-guide lasers are callerfiber lasers.

Neodymium is a common "dopant" in various solid-state lasercrystals, including yttrium orthovanadate (Nd:YVO4), yttrium lithium

fluoride (Nd:YLF) and yttrium aluminium garnet (Nd:YAG). All theselasers can produce high powers in the infrared spectrum at 1064 nm.They are used for cutting, welding and marking of metals and othermaterials, and also in spectroscopy and for pumping dye lasers.These lasers are also commonly frequency doubled, tripled orquadrupled to produce 532 nm (green, visible), 355 nm (UV) and266 nm (UV) light when those wavelengths are needed.

FIBER-HOSTED LASERS

Solid-state lasers where the light is guided due to the total internalreflection in an optical fiberare called fiber lasers. Guiding of lightallows extremely long gain regions providing good cooling conditions;fibers have high surface area to volume ratio which allows efficientcooling. In addition, the fiber's wave guiding properties tend to reducethermal distortion of the beam. Erbium and ytterbium ions arecommon active species in such lasers.

Quite often, the fiber laser is designed as a double-clad fiber. This

type of fiber consists of a fiber core, an inner cladding and an outercladding. The index of the three concentric layers is chosen so thatthe fiber core acts as a single-mode fiber for the laser emission whilethe outer cladding acts as a highly multimode core for the pump laser.This lets the pump propagate a large amount of power into andthrough the active inner core region, while still having a highnumerical aperture (NA) to have easy launching conditions.
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Fiber lasers have a fundamental limit in that the intensity of the lightin the fiber cannot be so high that optical nonlinearities induced bythe local electric field strength can become dominant and preventlaser operation and/or lead to the material destruction of the fiber..

PHOTONIC CRYSTEL LASER

Photonic crystal lasers are lasers based on nano.-structures thatprovide the mode confinement and the density of optical states (DOS)structure required for the feedback to take place. They are typicalmicrometer-sized and tunable on the bands of the photonic crystals.

SEMICONDUCTOR LASERS

Semiconductor lasers are also solid-state lasers but have a different

mode of laser operation.

Commercial laser diodes emit at wavelengths from 375 nm to1800 nm, and wavelengths of over 3 m have been demonstrated.Low power laser diodes are used in laser printers and CD/DVDplayers. More powerful laser diodes are frequently used to opticallypump other lasers with high efficiency. The highest power industriallaser diodes, with power up to 10 kW (70dBm), are used in industryfor cutting and welding. External-cavity semiconductor lasers have a

semiconductor active medium in a larger cavity. These devices cangenerate high power outputs with good beam quality, wavelength-tunable narrow-line width radiation, or ultra short laser pulses.

Vertical cavity surface-emitting lasers (VCSELs) are semiconductorlasers whose emission direction is perpendicular to the surface of thewafer. VCSEL devices typically have a more circular output beamthan conventional laser diodes, and potentially could be muchcheaper to manufacture. As of 2005, only 850 nm VCSELs are widelyavailable, with 1300 nm VCSELs beginning to be commercialized and

1550 nm devices an area of research. VECSELs are external-cavityVCSELs. Quantum cascade lasers are semiconductor lasers thathave an active transition between energy sub-bands of an electron ina structure containing several quantum wells.

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DYE LASERS

Dye lasers use an organic dye as the gain medium. The wide gainspectrum of available dyes allows these lasers to be highly tunable,

or to produce very short-duration pulses (on the order ofa few femto seconds).

FREE ELECTRON LASERS

Free electron lasers, or FELs, generate coherent, high powerradiation, that is widely tunable, currently ranging in wavelengthfrom microwaves, through terahertz radiation and infrared, to thevisible spectrum, to soft X-rays. They have the widest frequency

range of any laser type. While FEL beams share the same opticaltraits as other lasers, such as coherent radiation, FEL operation isquite different. Unlike gas, liquid, or solid-state lasers, which relyon bound atomic or molecular states, FELs use a relativisticelectron beam as the lasing medium, hence the term free electron.

RECENT INNOVATIONSSince the early period of laser history, laser research has

produced a variety of improved and specialized laser types,optimized for different performance goals, including:

new wavelength bands

maximum average output power

maximum peak output power

minimum output pulse duration

maximum power efficiency

maximum charging

minimum cost
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And this research continues to this day.

APPLICATIONS

Medicine: Bloodless surgery, laser healing, surgicaltreatment, kidney stone treatment, eye treatment, dentistry

Industry: Cutting, welding, material heat treatment, markingparts

Defense: Marking targets, guiding munitions, missiledefence, electro-optical countermeasures (EOCM),

alternative to radar

Research: Spectroscopy, laser ablation, Laser annealing, laserscattering, laser interferometry, LIDAR, Laser capturemicrodissection

Product development/commercial: laser printers, CDs,barcode scanners, thermometers, laser pointers, holograms,bubblegrams.

Laser lighting displays: Laser light shows

Laser skin procedures such as acne treatment, cellulitereduction, and hair removal.

In 2004, excluding diode lasers, approximately 131,000lasers were sold worldwide, with a value of US$2.19billion.In the same year, approximately 733 million diodelasers, valued at $3.20 billion, were sold.
http://wiki/Medicinehttp://wiki/Bloodless_surgeryhttp://wiki/Surgeryhttp://wiki/Surgeryhttp://wiki/Kidney_stonehttp://wiki/Laser_eye_surgeryhttp://wiki/Dentistryhttp://wiki/Industryhttp://wiki/Weldinghttp://wiki/Defense_(military)http://wiki/Munitionhttp://wiki/Airborne_Laserhttp://wiki/Airborne_Laserhttp://wiki/DIRCMhttp://wiki/Radarhttp://wiki/Researchhttp://wiki/Spectroscopyhttp://wiki/Laser_ablationhttp://wiki/Annealinghttp://wiki/Scatteringhttp://wiki/Interferometryhttp://wiki/LIDARhttp://wiki/Laser_capture_microdissectionhttp://wiki/Laser_capture_microdissectionhttp://wiki/Laser_printerhttp://wiki/Compact_dischttp://wiki/Barcodehttp://wiki/Thermometerhttp://wiki/Laser_pointerhttp://wiki/Hologramshttp://wiki/Bubblegramhttp://wiki/Laser_lighting_displayhttp://wiki/Laser_hair_removalhttp://wiki/Laser_hair_removalhttp://wiki/Laser_lighting_displayhttp://wiki/Bubblegramhttp://wiki/Hologramshttp://wiki/Laser_pointerhttp://wiki/Thermometerhttp://wiki/Barcodehttp://wiki/Compact_dischttp://wiki/Laser_printerhttp://wiki/Laser_capture_microdissectionhttp://wiki/Laser_capture_microdissectionhttp://wiki/Laser_capture_microdissectionhttp://wiki/LIDARhttp://wiki/Interferometryhttp://wiki/Scatteringhttp://wiki/Annealinghttp://wiki/Laser_ablationhttp://wiki/Spectroscopyhttp://wiki/Researchhttp://wiki/Radarhttp://wiki/DIRCMhttp://wiki/Airborne_Laserhttp://wiki/Airborne_Laserhttp://wiki/Airborne_Laserhttp://wiki/Munitionhttp://wiki/Defense_(military)http://wiki/Weldinghttp://wiki/Industryhttp://wiki/Dentistryhttp://wiki/Laser_eye_surgeryhttp://wiki/Kidney_stonehttp://wiki/Surgeryhttp://wiki/Surgeryhttp://wiki/Surgeryhttp://wiki/Bloodless_surgeryhttp://wiki/Medicine


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LASER AS A POWER

Different uses need lasers with different output powers. Lasers thatproduce a continuous beam or a series of short pulses can be

compared on the basis of their average power. Lasers that producepulses can also be characterized based on the peakpower of eachpulse. The peak power of a pulsed laser is many orders ofmagnitude greater than its average power. The average outputpower is always less than the power consumed.

The continuous or average power required for some uses:

1. less than 1 mW laser pointers

2.5 mW CD-ROM drive

3.510 mW DVD player or DVD-ROM drive

4.100 mW High-speed CD-RW burner

5.250 mW Consumer DVD-R burner

6.1 W green laser in current Holographic Versatile Discprototype development

Examples of pulsed systems with high peak power:

1.700 TW (7001012 W) National Ignition Facility, a 192-beam, 1.8-megajoule laser system adjoining a 10-meter-diameter target chamber.

PW (1.31015 W) world's most powerful laser as of 1998,located at the Lawrence Livermore Laboratory.
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LASER AS A WEAPON

Laser beams are famously employed as weapon systems in sciencefiction, but actual laser weapons are only beginning to enter the

market. The general idea of laser-beam weaponry is to hit a targetwith a train of brief pulses of light. The rapid evaporation andexpansion of the surface causes shockwaves that damage the target.

Lasers of all but the lowest powers can potentially be used asincapacitating weapons, through their ability to produce temporary orpermanent vision loss in varying degrees when aimed at the eyes.The degree, character, and duration of vision impairment caused byeye exposure to laser light varies with the power of the laser, thewavelength(s), the collimation of the beam, the exact orientation of

the beam, and the duration of exposure. Lasers of even a fraction ofa watt in power can produce immediate, permanent vision loss undercertain conditions, making such lasers potential non-lethal butincapacitating weapons. The extreme handicap that laser-inducedblindness represents makes the use of lasers even as non-lethalweapons morally controversial.

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REF.

www.en.wikipedia.org

www.answers.yahoo.com

www.howstuffworks.com

www.scienceworld.com

HIGHER ENGINEERING PHYSICS (BOOK).

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THANK YOU
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