Research for Lasers

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History of lasers

History of LasersInventors: Gordon Gould, Charles Townes, Arthur Schawlow, Theodore MaimanBy Mary Bellis, Aout!com Guide

The name LASERis an acronym for Li"ht Am#lification y the Stimulated Emissionof Radiation! In $%$&, Alert 'insteinfirst theori(ed aout the #rocess which ma)eslasers #ossile called *Stimulated 'mission!*Before the Laser there was the MaserIn $%+, Charles Townes and Arthur Schawlow invented the maser-microwaveam#lification y stimulated emission of radiation., usin" ammonia "as andmicrowave radiation / the maser was invented efore the -o#tical. laser! Thetechnolo"y is very close ut does not use a visile li"ht!0n March 1, $%+%, Charles Townes and Arthur Schawlow were "ranted a #atent forthe maser! The maser was used to am#lify radio si"nals and as an ultrasensitivedetector for s#ace research!

In $%+2, Charles Townes and Arthur Schawlow theori(ed and #ulished #a#ers aouta visile laser, an invention that would use infrared and3or visile s#ectrum li"ht,however, they did not #roceed with any research at the time!Many different materials can e used as lasers! Some, li)e the ruy laser, emit short

#ulses of laser li"ht! 0thers, li)e helium/neon "as lasers or li4uid dye lasers emit acontinuous eam of li"ht! See / How a Laser 5or)s6uy LaserIn $%78, Theodore Maiman invented the ruy laserconsidered to e the firstsuccessful o#tical or li"ht laser!Many historians claim that Theodore Maiman invented the first o#tical laser,however, there is some controversy that Gordon Gould was the first!Gordon Gould / LaserGordon Gould was the first #erson to use the word *laser*! There is "ood reason to

elieve that Gordon Gouldmade the first li"ht laser! Gould was a doctoral student atColumia 9niversity under Charles Townes, the inventor of the maser! Gordon Gouldwas ins#ired to uild his o#tical laser startin" in $%+2! He failed to file for a #atent hisinvention until $%+%! As a result, Gordon Goulds #atent was refused and histechnolo"y was e;#loited y others! It too) until $%&& for Gordon Gould to finallywin his #atent war and receive his first #atent for the laser!

Nobel Prizes in Physics

5e tend to use thin"s without thin)in" aout them! Has it ever occurred to you thatevery time you listen to a C< or #oint with a laser #ointer, you are holdin" thediscovery of a =oel >ri(e Laureate in >hysics, in your hand? 5ell, if you havent,youre not really alone!1964

Townes, Basovand Prokhorovshared the #ri(e for their fundamental wor), whichled to the construction of lasers! They founded the theory of lasers and descried howa laser could e uilt, ori"inatin" from a similar a##liance for microwaves called theMAS'6 that was introduced durin" the +8s -The MAS'6 has not een used as much

as the laser.!However, the first functionin" laser was not uilt y them, ut y aimanin $%78!
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Al-erovand .roemerwere "iven the #ri(e for their develo#ment within the field ofsemiconductor #hysics, where they had studied the ty#e of sustances that was firstused to uild semiconductor lasers, that is, the )ind of miniature lasers that today have

ecome the chea#est, li"htest and smallest! The idea is to #roduce oth the li"htsource and ener"y su##ly and #lace the mirrors in one crystal -less than $ mm facet,

with many se4uences.! This has ecome not only the asis for many chea# and#ortale a##liances, ut also the foundation in o#tical information networ)s!

How does this affect you?The C< #layer, laser writer, laser #ointer and the ar code reader the cashier at thesu#ermar)et uses, are all ased on their discovery!

LASER /0STR2

Stimulated 'mission / $%$&Alert 'insteinfirst #ro#osed the #rocess that ma)es lasers #ossile called*Stimulated 'mission!*

Holo"ra#hy / $%&Gaordevelo#ed the theory of holo"ra#hy, that re4uires laser li"ht for itsreali(ation!He received the $%&$ =oel >ri(e in >hysics for this wor)!

Maser / $%+The first #a#ers aout the maser were #ulished in $%+ as a result ofinvesti"ations carried out simultaneously and inde#endently y Townesand hisco/wor)ers at Columia 9niversity in =ew Dor) and y Basovand >ro)horovat the Leedev Institute in Moscow! Their wor) continued throu"hout the 78sand the &8s!Eor this wor) they were awarded the $%7 =oel >ri(e in >hysics!

Laser / $%+2The o#tical maser or the laser dates from $%+2, when the #ossiilities ofa##lyin" the maser #rinci#le in the o#tical re"ion were analy(ed y Schawlowand Townesas well as in the Leedev Institute! Laser s#ectrosco#y wasdevelo#ed y Schawlowand his co/wor)ers at Stanford 9niversity and, aroundthe same time, Bloemer"enand his co/wor)ers develo#ed nonlinear o#ticswhich is a very s#ecial a##lication of lasers#ectrosco#y!Eor this they were awarded the $%2$ =oel >ri(e in >hysics!

6uy Laser / $%78The first laser was o#eratin" in $%78! It was a ruy laser "eneratin" stron"

#ulses of red li"ht!Semiconductor / $%7Alferovand Froemer#ro#osed in $%7, inde#endently of each other, the

#rinci#le for semiconductor heterostructures to e used later in semiconductorlaser which today, y far, is the most common laser!Eor this wor) they were awarded the 1888 =oel >ri(e in >hysics!

Cornin" Glass / $%&80#tic fier made of cornin" "lass has such low losses that tele#hone calls andtelecommunication can e transferred for )ilometers with the hel# of laserli"ht!

Laser Coolin" / $%28In the 28s Chu, Cohen/Tannoud@iand >hilli#swor)ed with laser coolin" of
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atoms!Eor this wor) they were awarded the $%%& =oel >ri(e in >hysics!

The #hysicist Alert 'insteinhad descried the theory of stimulated emissionas early as $%$&, ut it would still ta)e 8 years efore en"ineers e"an toutili(e this #rinci#le for #ractical #ur#oses! Scientists were ama(ed y thistechnical rea)throu"h ut laser technolo"y itself had no real #ur#ose! This isnot e;ce#tional, discoveries may need time efore ein" #ut to use! Today laseris used in communication, industry, medicine, and environmental care andresearch! Laser has ecome one of the most #owerful tools for scientists in

#hysics, chemistry, iolo"y and medicine throu"hout the world! 0ne area thatis considered to e very interestin" is in the different methods to cool andca#ture atoms y usin" laser! 5e dont )now yet what this )nowled"e andtechnolo"y will e used for in the future, ut we do )now that futurea##lications will e ased on todays research!

3ha is a Laser5

Most #eo#le )now the word laser, ut do they )now what it really is? 5hats thedifference etween ordinary li"ht and laser and what does laser really stand for? Letsstart with the last 4uestion! Laser is an acronym, which is a word made u# of initialletters! Dou could use the com#lete name: li"ht am#lification y stimulated emissionof radiation ut thats a it aw)ward, lets )ee# to laser!

Almost everyone #roaly )nows that the #olice use laser when they measure s#eed!

At least many drivers that have e;ceeded the s#eed limit )now aout it, ut how many)now that you also use laser several times durin" an ordinary day? Doull find it inC< #layers, laser #rinters and much, much more!

Dou often find laser in action movies where the hero has to esca#e the laser eamswhen hes tryin" to solve a thrillin" #rolem! The #ower contained in laser is othfascinatin" and fri"htenin"!/ow oes Laser Li$h i--er -rom her Li$h5

Li"ht is really an electroma"netic wave! 'ach wave has ri"htness and color, andvirates at a certain an"le, so/called #olari(ation! This is also true for laser li"ht ut itis more #arallel than any other li"ht source! 'very #art of the eam has -almost. thee;act same direction and the eam will therefore diver"e very little! 5ith a "ood laseran o@ect at a distance of $ )m -8!7 mile. can e illuminated with a dot aout 78 mm-1! inches. in radius!

As it is so #arallel it can also e focused to very small diameters where theconcentration of li"ht ener"y ecomes so "reat that you can cut, drill or turn with the

eam! It also ma)es it #ossile to illuminate and e;amine very tiny details! It is this#ro#erty that is used in sur"ical a##liances and in C< #layers!

It can also e made very monochromic, so that @ust one li"ht wavelen"th is #resent!

This is not the case with ordinary li"ht sources! 5hite li"ht contains all the colors inthe s#ectrum, ut even a colored li"ht, such as a red L'< -li"ht emittin" diode.
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contains a continuous interval of red wavelen"ths!0n the other hand, laser emissions are not usually very stron" when it comes toener"y content! A very #owerful laser of the )ind that is used in a laser show does not"ive off more li"ht than an ordinary streetli"ht the difference is in how #arallel it is!Sim&lae( Emission

=ormally atoms and molecules emit li"ht at more or less random times and in randomdirections and #hases! All li"ht created in normal li"ht sources, such as uls, candles,neon tues and even the sun is "enerated in this way!

If ener"y is stored in the atom and li"ht of the correct wavelen"th #asses close ysomethin" else can ha##en! The atom emits li"ht that is totally synchronous with the

#assin" li"ht! This means that the #assin" li"ht has een am#lified which is necessaryfor the oscillation ta)in" #lace etween the mirrors in a laser!

Li"ht is normally emitted from atoms or molecules that meet with two conditions!/ They have stored ener"y ori"inatin" from heat or #revious asor#tion of li"ht/ A time has #assed since the ener"y was storedLi"ht emitted in this way "oes in random directions, with random #hases and at

random times!

Alert 'instein #redicted early in the $%88s that there is also another way for li"ht toe emitted! It can am#lify a #assin" eam, #rovided three conditions are met:/ 'ner"y is stored in the atom -same as aove./ Li"ht #asses close enou"h to the atom efore the time has e;#ired and the li"ht isemitted in the random fashion descried aove/ The #assin" li"ht has a wavelen"th suitale for the atom!

The #rocess ta)in" #lace in this case is called Stimulated 'mission, which, to"etherwith feedac) in a resonant cavity etween mirrors, forms the conditions for laser!

A cited and researched article tracin" the ori"in and history of the LAS'6 from radartechnolo"y -MAS'6s.includin" ma@or advancements over the years!LAS'6 is an acronym for Li"ht Am#lification y the Stimulated 'mission of6adiation! The conce#t consists of an e;cited state atom encounterin" a #hoton of thesame ener"ythat corres#onds to the


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scientists e"in to create inverted #o#ulations with more atoms in the e;cited statethan the "round state so that asor#tion would not dominate the #rocess andstimulated emission could occur!The #recursor to the laser was the maser! The maser am#lified electroma"neticradiation of much shorter wavelen"ths in the microwave ran"e -thus the M instead of

L in maser.! The im#etus for the develo#ment of the maser seems to e the interest inmicrowave radiation followin" the utility it found in radar technolo"y in 5orld 5arII! After the war, many scientists who had wor)ed on develo#in" the radar continuedtheir investi"ations into microwave radiation usin" much of the military sur#lusmicrowave e4ui#ment! The first maser was created y Charles H! Townes -#ulishedin $%+. who alon" with ames Gordon and Herert ei"er succeeded in #roducin" aninverted #o#ulation y isolatin" e;cited ammonia molecules! The e;cited moleculeswere aimed into a cavity resonant at the 1/"i"ahert( fre4uency of the ammoniatransition where stimulated emission occurred! Since there was a #hysical se#arationof e;cited state molecules, however, after emission, the maser action ended! Thus thefirst maser was inca#ale of continuous out#ut! In order to achieve continuous out#ut,

new systems with more than two ener"y levels had to e desi"ned! These systemscould release stimulated emission without fallin" to the "round state, thus maintainin"a #o#ulation inversion! =i)olai Basov and Ale;ander >ro)horov of the 9SS6 firstdevelo#ed this idea! To"ether, Basov, >ro)horov, and Townes shared the $%7 =oel>ri(e in >hysics for develo#in" the maser conce#t!Soon after masers ecame a reality, #eo#le e"an to loo) at the #ossiility ofstimulated emission in other re"ions of theelectroma"netic s#ectrum!Townes, alon"with Arthur Schawlow, e"an investi"atin" the #ossiility of o#tical and I6 masers!To"ether they #ulished the first detailed #ro#osal for uildin" an o#tical maser -laterto e renamed a laser. in a hysical 6eview! The ostacles tocreatin" a wor)in" laser, however were "reat! The much smaller wavelen"ths ofvisile li"ht and the difficulty of findin" an a##ro#riate e;citation medium meant thatmuch more accurate measurements needed to e made and that error in settin" u# thea##aratus had a much more crucial effect on the function of a laser! It was not until$%78 that Theodore Maiman created the first wor)in" laser! Maimans laser was a*#in)* ruy rod with its ends silvered #laced inside a s#rin"/sha#ed flashlam#!Maimans laser, however, was only ca#ale of #ulsed o#eration due to its ener"ylevel transitions! Soon afterwards, in $%78, >eter Soro)in and Mire) Stevensondevelo#ed the first level laser -uranium do#ed calcium floride. which was ca#alein theory of continuous out#ut althou"h in solid state, a continuous out#ut could not

e achieved! The develo#ment of laser technolo"y had e"un!

ust efore the end of $%78 -#ulished $%7$., Ali avan, 5illiam Bennet, and atel e"an wor)in" with caron dio;ide -#ulished $%7. and caron mono;idelasers which he mi;ed with nitro"en, helium and water to fine tune the laser

#ro#erties! Thus >atel made the first hi"h #owered "as lasers! 'arl Bell then

discovered the ion laser when he #laced mercury ions in helium to create lasin" action-#ulished $%7.! Althou"h the mercury ion laser has never seen much a##lication, it
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was a direct #redecessor to the ar"on/ion laser develo#ed y 5illiam Brid"es! The"as ion lasers then led to the develo#ment of metal va#or lasers y many #eo#le whowor)ed with different metal va#ors!Some further laser develo#ments were as follows: usin" chemical reactions instead ofelectric currents to "enerate a lasin" effect, usin" ra#id coolin" throu"h e;#ansion to

cause e;citation, usin" dyes as a medium to tune the laser across a ran"e ofwavelen"ths, and usin" #/n @unctions in semiconductors or a free electron medium tocreate lasin" effects!Juic)ly after their ince#tion the utility of lasers were reali(ed and their conceiveduses s)yroc)eted! After around $%7, however, e;citement aout lasers e"an tosuside! Althou"h new uses had een conceived for them, some of the #ro@ecteda##lications were #rovin" difficult to achieve and many lasers were #rovin" difficultto ma)e! Eor instance, there was little success in develo#in" a continuous, room/tem#erature semiconductor laser for com#utin" #ur#oses! Laser #ower also seemedlimited, disillusionin" the 9!S! "overnment in its #otential military a##lications!Lasers were dued *a solution loo)in" for a #rolem!* The first uses of lasers

consisted more or less of re#lacin" less efficient li"ht sources, i!e! ;enon arc lam#s in#hotocoa"ulators and mercury arcs in interferometers! Laser research slowlycontinued and increased its readth! There were a variety of im#rovements in laserdesi"n which increased laser lifetime, focused eam width, im#roved continuity ofout#ut, re"ulated and shortened #ulse duration, etc! Anthony


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5ith increasin" #ower and decreasin" #ulse duration -the develo#ments associatedwith C!F!=! >atel and Anthony


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radiation, however, creates a means for inducin" and monitorin" ultrafast#hotochemical reactions! It is #ossile to identify short/lived intermediate s#ecies insolution with lasers that have ever/decreasin" #ulse duration! There has even eensome #ro"ress in monitorin" the rotational and steric action as well aselectrontransfer rates of s#ecies in solution usin" #icosecond and femtosecond laser

techni4ues!The future of lasers is a #romisin" one! ud"in" from the 4uic) develo#ment of lasersin the #ast and continuin" laser research, there does not a##ear to e a slowin" oflaser research in the near future! Althou"h lasers have found use in s#ectrosco#ictechni4ues, it is really the new methods that resulted from laser develo#ment thatindicate the #otential fruitfulness of laser research! Laser induced #hotochemistry, themonitorin" of chemical intermediates with #icosecond and femtosecond lasers, andnonlinear s#ectrosco#y re#resent merely the e"innin" of innovative techni4ues forlasers in chemistry! As time #ro"resses, there will doutless e new scientists withnew ideas and new e;#eriments which will e;#and the role of lasers in chemicalresearch!

6eferences-$. htt#:33www!achilles!net3K@talot3history3inde;!html-1. Andrews, ress, Camrid"e,MA, $%%$.!-+. 'vans, hysical Chemistry! -Marcel artB / ';#erimental Techni4ues and Medium 'ffects! -'lsevier, =ew Dor), $%22.!-2. Gordon, !>! ei"er, H!! Townes, C!H! >hys! 6ev!, %+, 121, $%+!-%. Hecht, eff! Laser >ioneers! -Academic >ress, Boston, $%%1.!-$8. Maiman, T!H! =ature! $2&, %, $%78!
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$%$& Theory o- sim&lae( emission

Alert 'instein #ro#oses the theory of stimulated emissionNthat is, if an atom in ahi"h/ener"y state is stimulated y a #hoton of the ri"ht wavelen"th, another #hoton ofthe same wavelen"th and direction of travel will e created! Stimulated emission willform the asis for research into harnessin" #hotons to am#lify the ener"y of li"ht!

$%+ 7aser7 (evelo*e(

Charles Townes, ames Gordon, and Herert ei"er at Columia 9niversity develo# a*maser* -for microwave am#lification y stimulated emission of radiation., in whiche;cited molecules of ammonia "as am#lify and "enerate radio waves! The wor) ca#s years of effort since Towness idea in $%+$ to ta)e advanta"e of hi"h/fre4uency

molecular oscillation to "enerate short/wavelen"th radio waves!

$%+2 %once* o- a laser inro(&ce(

Townes and #hysicist Arthur Schawlow #ulish a #a#er showin" that masers could emade to o#erate in o#tical and infrared re"ions! The #a#er e;#lains the conce#t of alaser -li"ht am#lification y stimulated emission of radiation.Nthat li"ht reflected

ac) and forth in an ener"i(ed medium "enerates am#lified li"ht!

$%78 *erable laser invene(

Theodore Maiman, a #hysicist and electrical en"ineer at Hu"hes 6esearchLaoratories, invents an o#erale laser usin" a synthetic #in) ruy crystal as the

medium! 'ncased in a *flash tue* and oo) ended y mirrors, the laser successfully#roduces a #ulse of li"ht! >rior to MaimanOs wor)in" model, Columia 9niversity


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doctoral student Gordon Gould also desi"ns a laser, ut his #atent a##lication isinitially denied! Gould finally wins #atent reco"nition nearly 8 years later!

$%78 %onin&o&sly o*erain$ heli&m'neon $as laser invene(

Bell Laoratories researcher and former Townes student Ali avan and his collea"ues

5illiam Bennett, r!, and resyterian Medical Center and Charles Foester of theAmerican 0#tical Cor#oration use a #rototy#e ruy laser #hotocoa"ulator to destroy ahuman #atientOs retinal tumor!

$%71 "alli&m arseni(e laser (evelo*e(

Three "rou#sNat General 'lectric, IBM, and MITOs Lincoln LaoratoryNsimultaneously develo# a "allium arsenide laser that converts electrical ener"ydirectly into infrared li"ht and that much later is used in C< and hysicist Herert Froemer #ro#oses the idea of heterostructures, cominations ofmore than one semiconductor uilt in layers that reduce ener"y re4uirements forlasers and hel# them wor) more efficiently! These heterostructures will later e usedin cell #hones and other electronic devices!

$%77 Lan(mark *a*er on o*ical -iber

Charles Fao and Geor"e Hoc)ham of Standard Telecommunications Laoratories in'n"land #ulish a landmar) #a#er demonstratin" that o#tical fier can transmit laser

si"nals with much reduced loss if the "lass strands are #ure enou"h! 6esearchersimmediately focus on ways to #urify "lass!

$%&8 *ical -ibers ha mee *&riy san(ar(s

Cornin" Glass 5or)s scientists eter Schult(, and 6oert Maurerre#ort the creation of o#tical fiers that meet the standards set y Fao and Hoc)ham!The #urest "lass ever made, it is com#osed of fused silica from the va#or #hase ande;hiits li"ht loss of less than 18 deciels #er )ilometer -$ #ercent of the li"ht remainsafter travelin" $ )ilometer.! By $%&1 the team creates "lass with a loss of deciels

#er )ilometer! Also in $%&8, Morton >anish and I(uo Hayashi of Bell Laoratories,alon" with a "rou# at the Ioffe >hysical Institute in Lenin"rad, demonstrate a

semiconductor laser that o#erates continuously at room tem#erature! Bothrea)throu"hs will #ave the way toward commerciali(ation of fier o#tics!


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$%& %hemical va*or (e*osiion *rocess

ohn MacChesney and >aul 0OConnor at Bell Laoratories develo# a modifiedchemical va#or de#osition #rocess that heats chemical va#ors and o;y"en to formultratrans#arent "lass that can e mass/#roduced into low/loss o#tical fier! The

#rocess still remains the standard for fier/o#tic cale manufacturin"! $%&+ 8irs commercial semicon(&cor laser

'n"ineers at Laser that year from the 0lym#ic Games in La)e >lacid, =ew Dor)! Two years later MCIannounces a similar #ro@ect usin" sin"le/mode fier carryin" 88 its #er second!

$%2& 7o*e(7 -iber am*li-iers

ayne at 'n"landOs 9niversity of Southam#ton introduces fier am#lifiers thatare *do#ed* with the element erium! These new o#tical am#lifiers are ale to oostli"ht si"nals without first havin" to convert them into electrical si"nals and then ac)into li"ht!

$%22 8irs ransalanic -iber'o*ic cable

The first transatlantic fier/o#tic cale is installed, usin" "lass fiers so trans#arent

that re#eaters -to re"enerate and recondition the si"nal. are needed only aout 8miles a#art! The shar)/#roof TAT/2 is dedicated y science fiction writer IsaacAsimov, who #raises *this maiden voya"e across the sea on a eam of li"ht!* Lin)in"

=orth America and Erance, the ,$2/mile cale is ca#ale of handlin" 8,888tele#hone calls simultaneously usin" $!/micrometer wavelen"th lasers and sin"le/mode fier! The total cost of P7$ million is less than P$8,888 #er circuit the firsttransatlantic co##er cale in $%+7 costs P$ million #er circuit to #lan and install!

$%%$ *ical Am*li-iers

'mmanuel


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$%%7 All'o*ic -iber cable ha &ses o*ical am*li-iers is lai( across he Paci-iccean

T>C/+, an all/o#tic fier cale that is the first to use o#tical am#lifiers, is laid in aloo# across the >acific 0cean! It is installed from San Luis 0is#o, California, to

Guam, Hawaii, and Miya(a)i, a#an, and ac) to the 0re"on coast and is ca#ale ofhandlin" 18,888 simultaneous tele#hone calls!

$%%& 8iber *ic Link Aro&n( he "lobe

The Eier 0#tic Lin) Around the Gloe -ELAG. ecomes the lon"est sin"le/calenetwor) in the world and #rovides infrastructure for the ne;t "eneration of Interneta##lications! The $&,+88/mile cale e"ins in 'n"land and runs throu"h the Strait ofGiraltar to >alermo, Sicily, efore crossin" the Mediterranean to '"y#t! It then "oesoverland to the ELAG o#erations center in hysical events are to ethou"ht of as movements accordin" to law of material #ointsin s#ace! The material
http://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Sir_Isaac_Newtonhttp://en.wikipedia.org/wiki/Sir_Isaac_Newtonhttp://en.wikipedia.org/wiki/Sir_Isaac_Newtonhttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Corpuscularianismhttp://en.wikipedia.org/wiki/Speed_of_lighthttp://en.wikipedia.org/wiki/Speed_of_lighthttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/Wave%E2%80%93particle_dualityhttp://en.wikipedia.org/wiki/Christiaan_Huygenshttp://www.gutenberg.org/files/14725/14725-h/14725-h.htmhttp://www.gutenberg.org/files/14725/14725-h/14725-h.htmhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Corpuscular_theory_of_light#cite_note-0http://en.wikipedia.org/wiki/Albert_Einsteinhttp://en.wikipedia.org/wiki/Albert_Einsteinhttp://en.wikipedia.org/wiki/Albert_Einsteinhttp://en.wikipedia.org/wiki/Space#Physicshttp://en.wikipedia.org/wiki/Timehttp://en.wikipedia.org/wiki/Timehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Sir_Isaac_Newtonhttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Corpuscularianismhttp://en.wikipedia.org/wiki/Speed_of_lighthttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Photoelectric_effecthttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Quantum_mechanicshttp://en.wikipedia.org/wiki/Wave%E2%80%93particle_dualityhttp://en.wikipedia.org/wiki/Christiaan_Huygenshttp://www.gutenberg.org/files/14725/14725-h/14725-h.htmhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Interference_(wave_propagation)http://en.wikipedia.org/wiki/Polarization_(waves)http://en.wikipedia.org/wiki/Corpuscular_theory_of_light#cite_note-0http://en.wikipedia.org/wiki/Albert_Einsteinhttp://en.wikipedia.org/wiki/Space#Physicshttp://en.wikipedia.org/wiki/Timehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particle


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#ointis the only re#resentative of reality in so far as it is su@ect to chan"e! Theconce#t of the material #ointis oviously due to oservaleodies one conceived ofthe material #oint on the analo"y of movale odies y omittin" characteristics ofe;tension, form, s#atial locality, and all their inner 4ualities, retainin" onlyinertia,translation, and the additional conce#t of force!R1R

Model 0ne:Juantum Theory ofLi"htJuantum theory evolved as a new ranch of theoretical #hysics durin" the first fewdecades of the 18th century in an endeavour to understand the fundamental #ro#ertiesof matter! It e"an with the study of the interactions of matter and radiation! Certainradiation effects could neither e e;#lained y classical mechanics, nor y the theoryof electroma"netism! In #articular, #hysicists were #u((led y the nature of li"ht!>eculiar lines in the s#ectrum of sunli"ht had een discovered earlier y ose#h vonEraunhofer -$&2&/$217.! These s#ectral lines were then systematically catalo"ued forvarious sustances, yet noody could e;#lain why the s#ectral lines are there and whythey would differ for each sustance! It too) aout one hundred years, until a

#lausile e;#lanation was su##lied y 4uantum theory!Juantum theory is aout the nature of matter!In contrast to 'insteins 6elativity, which is aout the lar"est thin"s in the universe,4uantum theory deals with the tiniest thin"s we )now, the #articles that atoms aremade of, which we call *suatomic* #articles! In contrast to 6elativity, 4uantumtheory was not the wor) of one individual, ut the collaorative effort of some of themost rilliant #hysicists of the 18th century, amon" them =iels Bohr, 'rwinSchrdin"er, 5olf"an" >auli, and Ma; Born! Two names clearly stand out: Ma;>lanc) -$2+2/$%&. and 5erner Heisener" -$%8$/$%&7.! >lanc) is reco"nised as theori"inator of the 4uantum theory, while Heisener" formulated one of the mosteminent laws of 4uantum theory, the 9ncertainty >rinci#le, which is occasionally also

referred to as the #rinci#le of indeterminacy!>lanc)s constant: 'ner"y is not continuous!
http://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Physical_bodyhttp://en.wikipedia.org/wiki/Extension_(metaphysics)http://en.wikipedia.org/wiki/Substantial_formhttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Translation_(physics)http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Corpuscular_theory_of_light#cite_note-1http://en.wikipedia.org/wiki/Corpuscular_theory_of_light#cite_note-1http://en.wikipedia.org/wiki/Corpuscular_theory_of_light#cite_note-2http://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Point_particlehttp://en.wikipedia.org/wiki/Physical_bodyhttp://en.wikipedia.org/wiki/Extension_(metaphysics)http://en.wikipedia.org/wiki/Substantial_formhttp://en.wikipedia.org/wiki/Inertiahttp://en.wikipedia.org/wiki/Translation_(physics)http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Corpuscular_theory_of_light#cite_note-1http://en.wikipedia.org/wiki/Corpuscular_theory_of_light#cite_note-2


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Around $%88, Ma; >lanc) from the 9niversity of Fiel concerned himself withoservations of the radiation of heated materials! He attem#ted to draw conclusionsfrom the radiation to the radiatin" atom! 0n asis of em#irical data, he develo#ed anew formula which later showed remar)ale a"reement with accurate measurementsof the s#ectrum of heat radiation! The result of this formula was so that ener"y is

always emitted or asored in discrete units, which he called 4uanta! >lanc)develo#ed his 4uantum theory further and derived a universal constant, which came to

e )nown as >lanc)s constant! The resultin" law states that the ener"y of each4uantum is e4ual to the fre4uency of the radiation multi#lied y the universalconstant: 'UfVh, where h is 7!7 V $8'/ s! The discovery of 4uanta revolutionised

#hysics, ecause it contradicted conventional ideas aout the nature of radiation andener"y!The atom model of Bohr!To understand the "ist of the 4uantum view of matter, we have to "o ac) to the $%thcenturys #redominant model of matter! Scientists at the time elieved /li)e the Gree)atomists/ that matter is com#osed of indivisile, solid atoms, until 6utherford #roved

otherwise!The British #hysicist 'rnest 6utherford -$2&$/$%&. demonstrated e;#erimentallythat the atom is not solid as #reviously assumed, ut that it has an internal structureconsistin" of a small, dense nucleus aout which electrons circle in orits!

=iels Bohr -$22+/$%71. refined 6utherfords model yintroducin" different orits in which electrons s#in around the nucleus! This model isstill used in chemistry! 'lements are distin"uished y their *atomic numer*, whichs#ecifies the numer of #rotons in the nucleus of the atom! 'lectrons are held in theirorits throu"h the electrical attraction etween the #ositive nucleus and the ne"ativeelectron! Bohr ar"ued that each electron has a certain fi;ed amount of ener"y, whichcorres#onds to its fi;ed orit! Therefore, when an electron asors ener"y, it @um#s tothe ne;t hi"her orit rather than movin" continuously etween orits! Thecharacteristic of electrons havin" fi;ed ener"y 4uantities -4uanta. is also )nown as the4uantum theory of the atom!

The aove model ears a stri)in" similarity with the =ewtonian model of our solarsystem! 'lectrons revolve around the nucleus, @ust as #lanets revolve around the Sun!It is therefore not sur#risin" that #hysicists tried to a##ly classical mechanics to theatomic structure! The forces etween nucleus and electrons were e4uated with the"ravitational forces etween celestial odies! This idea wor)ed 4uite well for thehydro"en atom, the sim#lest of all elements, ut it failed to e;#lain the ehaviour ofmore com#le; atoms!If matter is not infinitely divisile, why should ener"y e?The idea that ener"y could e emitted or asored only in discrete ener"y 4uantaseemed odd, since it could not e fitted into the traditional framewor) of #hysics! The4uantum ehaviour of electrons in atoms contradicted not only classical mechanics,

ut also Ma;wells electroma"netic theory, which re4uired it to radiate away ener"ywhile oritin" in a 4uantum ener"y state! 'ven Ma; >lanc), who was a conservative


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man, initially douted his own discovery! The traditional view was that ener"y flowsin a continuum li)e a smooth, unro)en stream of water! That there should e "a#s

etween the discrete entities of ener"y seemed wholly unreasonale! In fact, >lanc)sidea only "ained credence when 'instein used it in $%8+ to e;#lain the #hotoelectriceffect! / After all, if matter is not infinitely divisile, why should ener"y e?

In the course of time, #hysicists descended dee#er into the realm of the atom! Bohrsatom model was remar)aly successful in descriin" the s#ectrum of the hydro"enatom y usin" >lanc)s formula to relate different ener"y levels of electrons todifferent fre4uencies of li"ht radiation! 9nfortunately, it did not wor) well for morecom#le; atoms, and so a more so#histicated theory had to e develo#ed! The #rolemseemed to e rooted in the assum#tion that an electron rotates around the nucleus li)ea massive o@ect revolves around a centre of "ravity!


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etween any two #ositions! The conce#t of causality cannot e a##lied to what isoserved! In case of the electrons of an atom, the closest we can "et to descriin" theelectrons #osition is y "ivin" a numer for the #roaility of it ein" at a #articular

#lace! Moreover, #articles have other *disturin"* #ro#erties: They have a tendency todecay into other #articles or into ener"y, and sometimes /under s#ecial circumstances/

they mer"e to form new #articles! They do so after indeterminate time s#ans!Althou"h we can ma)e statistical assertions aout a #articles lifetime, it is im#ossileto #redict the fate of an individual #article!5hat does 4uantum #hysics say aout the universe?Can we derive any new )nowled"e aout the universe from 4uantum #hysics? Afterall, the entire universe is com#osed of an unima"inale lar"e numer of matter andener"y! It seems to e of "reat im#ortance to understand 4uantum theory #ro#erly inview of the lar"e/scale structure of the cosmos! Eor e;am#le, an interestin" 4uestionin this conte;t is why the oservale matter in the universe is #ac)ed to"ether in"ala;ies and is not evenly distriuted throu"hout s#ace! Could it have to do with the4uantum characteristics of ener"y? Are 4uantum effects res#onsile for matter

formin" discrete entities, instead of s#readin" out evenly durin" the irth of theuniverse? The answer to this 4uestion is still ein" deated!If cosmolo"ical conclusions seem laoured, we mi"ht e ale to derive #hiloso#hicalinsi"hts from 4uantum #hysics! At least Erit@of Ca#ra thin)s this is #ossile when hedescries the #arallels etween modern #hysics and ancient 'astern #hiloso#hy in his

oo) The Tao of >hysics! He holds that in a way, the essence of modern #hysics iscom#arale to the teachin"s of the ancient 'astern #hiloso#hies, such as the ChineseTao Te Chin", the Indian 9#anishads, or the Buddhist Sutras! 'astern #hiloso#hiesa"ree in the #oint that ultimate reality is indescriale and una##roachale, not onlyin terms of common lan"ua"e, ut also in the lan"ua"e of mathematics! That is,science and mathematics must fail at some sta"e in descriin" ultimate reality! 5e seethis e;em#lified in the 9ncertainty >rinci#le, which is elucidated in the followin"section!Molecules and atoms cannot e s#lit into inde#endent units! All #arts interact at alllevels!The oriental scri#tures a"ree in the #oint that all oservale and descriale realitiesare manifestations of the same underlyin" *divine* #rinci#le! Althou"h many

#henomena of the oservale world are seemin"ly unrelated, they all "o ac) to thesame source! Thin"s are intertwined and interde#endent to an unfathomale de"ree,

@ust as the #articles in an atom are! Althou"h the electrons in an atom can e thou"htof as individual #articles, they are not really individual #articles, ecause of the

com#licated wave relations that e;ist etween them! Hence, the electron cloud modeldescries the atomic structure more ade4uately! The sum of electrons in an atomcannot e se#arated from its nucleus, which has a com#ound structure itself and canneither e re"arded a se#arate entity! Thus, in the multi#licity of thin"s there is unity!Matter is many thin"s and one thin" at the same time!The 'astern scri#tures say that no statement aout the world is ultimately valid -*TheTao that can e told is not the eternal Tao!* Tao Te Chin", erse $., since not eventhe most elaorate lan"ua"e is ca#ale of renderin" a #erfect model of the universe!Science is often com#ared to a tree that ranches out into many directions! Thedis#osition of #hysics is that it follows the tree u#ward to its ranches and leaves,while meta/#hysics follows it down to the root! 5hether the ranches of )nowled"e

stretch out indefinitely is still a matter of deate! However, it a##ears that mostscientific discoveries do not only answer 4uestions, ut also raise new ones!


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The German #hiloso#her, EriedrichHe"el formulated an idea at the e"innin" of the$%th century that descries this #rocess! He #ro#osed the dialectic triad of thesis,antithesis, and synthesis, in which an idea -thesis. always contains incom#letenessand thus yields a conflictin" idea -antithesis.! A third #oint of view -synthesis. arises,which overcomes the conflict y reconcilin" the truth contained in oth, thesis and

antithesis, at a hi"her level of understandin"! The synthesis then ecomes a newthesis, "enerates another antithesis, and the #rocess starts over! In the ne;t section, weshall see how 18th century #hysics emodies He"els dialectical #rinci#le! 5e willalso ta)e a close loo) at the #hiloso#hical im#lications of Heisener"s 9ncertainty>rinci#le!

6'E'6 T0 B00F

Model Two: Theoryof Stimulated'missionStimulated emission

0ne oson in a state can stimulate or induce another oson into the same state,causin" a 4uantum event -e"! an atomic transition.!*A s#lendid li"ht has dawned on me aout the asor#tion and emission of radiation!!!*Alber Einsein, letter to Michele An"elo Besso =ovemer $%$7

5hat 'instein had reali(ed is that li"ht shined on an atom which is in an e;cited statecan induce the atom to ma)e a downward transition -emittin" a #hoton. if theincomin" li"hts fre4uency matches the atomic transition ener"y! The incomin$

*hoon is a boson an( -or his reason i sim&laes he emission o- a secon(*hoon in he same sae, inducin" an atomic transition! -0therwise the *s#ontaneousemission* would ha##en randomly!.Thus, in stimulated emission we have an e;am#le of *4uantum causality!*This #rocess comined with reflection can yield many #hotons in the same state:coherent li"ht! Stimulated emission underlies the laser!

Actually, its allstimulated!!!

Erom the #oint of view of 4uantum field theory, even random 4uantum 4uantumevents such as so called s#ontaneous emission are really stimulated y the vacuums

zero *oin ener$y:
http://nonlocal.com/hbar/laser.htmlhttp://nonlocal.com/hbar/laser.htmlhttp://nonlocal.com/hbar/laser.html


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*5hen you come ri"ht down to it, there is really no such thing as trulys#ontaneousemission its allstimulated emission! The only distinction to e made is whether thefield that does the stimulatin" is one that you #ut there or one that God #ut there!!!*avi( "ri--hsIntroduction to Quantum Mechanics

*Erom the #ers#ective of 4uantum electrodynamics, s#ontaneous emission is a ty#e ofstimulated emission induced y fluctuations in the electroma"netic field of thevacuum! Confinin" an e;cited atom or molecule to a sufficiently small enclosuresi"nificantly modifies the fluctuations of the vacuum, and therefore also thes#ontaneous decay rate of a 4uantum state see redicts Stimulated 'mission

The laserOs invention launched a multi/illion dollar industry! Lasers are used toremove unwanted tattoos to correct vision defects in laser eye sur"ery to cut throu"hsteel and other materials in industrial assemly lines to scan #rices in su#ermar)etsand de#artment stores for o#tical communications and o#tical data stora"e and inelectronic devices li)e C< and


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emission! Atoms will only asor #hotons of the correct wavelen"th: the #hotondisa##ears and the atom "oes to a hi"her ener"y state, settin" the sta"e fors#ontaneous emission! Second, his theory #redicted that as li"ht #asses throu"h asustance, it could stimulate the emission of more li"ht!'instein #ostulated that #hotons #refer to travel to"ether in the same state! If one has a

lar"e collection of atoms containin" a "reat deal of e;cess ener"y, they will e readyto emit a #hoton randomly! However, if a stray #hoton of the correct wavelen"th

#asses y -or, in the case of a laser, is fired at an atom already in an e;cited state., its#resence will stimulate the atoms to release their #hotons earlyQand those #hotonswill travel in the same direction with the identical fre4uency and #hase as the ori"inalstray #hoton! A cascadin" effect ensues: as the crowd of identical #hotons movesthrou"h the rest of the atoms, ever more #hotons will e emitted from their atoms to

@oin them!It wasnOt until the $%8s and $%+8s that #hysicists found a use for the conce#t, eventhou"h all that was re4uired to invent a laser was findin" the ri"ht )ind of atom, andaddin" reflectin" mirrors to fortify the stimulated emission #rocess y #roducin" a

chain reaction! Charles Townes had wor)ed on radar systems durin" 5orld 5ar II!After the war ended, he turned his attention to molecular s#ectrosco#y, a techni4uethat studies the asor#tion of li"ht y molecules! ust li)e radar, moleculars#ectrosco#y omards the surface of molecules with li"ht and analy(es the scatteredradiation to determine the moleculeOs structure!But the techni4ue was limited y the wavelen"th of the li"ht #roduced: in this case,the microwave re"ime of the electroma"netic s#ectrum! Townes noticed that as thewavelen"th of the microwaves shortened, the more stron"ly the li"ht interacted withthe molecules, and the more one could learn aout them! He thou"ht it mi"ht e

#ossile to develo# a device that #roduced li"ht at much shorter wavelen"ths! Theest way to do this, he thou"ht, would e to use molecules to "enerate the desiredfre4uencies throu"h stimulated emission!Townes mentioned the idea to a collea"ue -later his rother/in/law., ArthurSchawlow, who #ro#osed that the #rototy#e laser e fitted with a #air of mirrors, oneat each end of the lasin" cavity! >hotons of s#ecific wavelen"ths would then reflectoff the mirrors and travel ac) and forth throu"h the lasin" medium! By doin" so,they would in turn cause other electrons to rela; ac) into their "round states,emittin" even more #hotons in the same wavelen"th! So only #hotons in the selectedwavelen"th and fre4uency ran"e would e am#lified!The two men wrote a #a#er detailin" their conce#t, #ulished in the


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Model Three: EirstLasers and LaserTheory

6uy laser


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A ruy laser rod! Inset: The view throu"h the rod is crystal clearSee also:

A ruy laser most often consists of a ruy rod that must e#um#edwith very hi"hener"y, usually from a flashtue, to achieve a#o#ulation inversion!The rod is often

#laced etween two mirrors, formin" ano#tical cavity, which oscillate the li"ht#roduced y the ruys fluorescence, causin"stimulated emission! 6uy is one of thefew solid state lasers that #roduce li"ht in the visile ran"e of the s#ectrum, lasin" at7%! nanometers, in a dee# red color, with a very narrow linewidth of 8!+ nm!The ruy laser is a three level solid state laser! Theactive laser medium-laser"ain3am#lificationmedium. is a synthetic ruyrod that is ener"i(ed throu"h o#tical

#um#in", ty#ically y a ;enonflashtue! 6uy has very road and #owerfulasor#tion ands in the visual s#ectrum, at 88 and ++8 nm, and a very lon"fluorescence lifetime of milliseconds! This allows for very hi"h ener"y #um#in",

since the #ulse duration can e much lon"er than with other materials! 5hile ruy hasa very wide asor#tion #rofile, its conversion efficiency is much lower than othermediums!In early e;am#les, the rods ends had to e #olished with "reat #recision, such that theends of the rod were flat to within a 4uarter of a wavelen"th of the out#ut li"ht, and

#arallel to each other within a few seconds of arc! The finely #olished ends of the rodwere silvered one end com#letely, the other only #artially! The rod, with its reflectiveends, then acts as aEaryQ>Yrot etalon-or aGires/Tournois etalon.! Modern lasersoften use rods with antireflection coatin"s, or with the ends cut and #olished atBrewsters an"leinstead! This eliminates the reflections from the ends of the rod!';ternal dielectric mirrorsthen are used to form the o#tical cavity! Curved mirrorsarety#ically used to rela; the ali"nment tolerances and to form a stale resonator, oftencom#ensatin" for thermal lensin" of the rod!
http://en.wikipedia.org/wiki/Laser_pumpinghttp://en.wikipedia.org/wiki/Flashtubehttp://en.wikipedia.org/wiki/Population_inversionhttp://en.wikipedia.org/wiki/Population_inversionhttp://en.wikipedia.org/wiki/Optical_cavityhttp://en.wikipedia.org/wiki/Optical_cavityhttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Stimulated_emissionhttp://en.wikipedia.org/wiki/Stimulated_emissionhttp://en.wikipedia.org/wiki/Population_inversion#Three-level_lasershttp://en.wikipedia.org/wiki/Active_laser_mediumhttp://en.wikipedia.org/wiki/Active_laser_mediumhttp://en.wikipedia.org/wiki/Active_laser_mediumhttp://en.wikipedia.org/wiki/Amplifierhttp://en.wikipedia.org/wiki/Synthetic_rubyhttp://en.wikipedia.org/wiki/Optical_pumpinghttp://en.wikipedia.org/wiki/Optical_pumpinghttp://en.wikipedia.org/wiki/Xenonhttp://en.wikipedia.org/wiki/Xenonhttp://en.wikipedia.org/wiki/Silveringhttp://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_etalonhttp://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_etalonhttp://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_etalonhttp://en.wikipedia.org/wiki/Gires-Tournois_etalonhttp://en.wikipedia.org/wiki/Gires-Tournois_etalonhttp://en.wikipedia.org/wiki/Antireflection_coatinghttp://en.wikipedia.org/wiki/Brewster's_anglehttp://en.wikipedia.org/wiki/Dielectric_mirrorhttp://en.wikipedia.org/wiki/Curved_mirrorhttp://en.wikipedia.org/wiki/File:Ruby_transmittance.svghttp://en.wikipedia.org/wiki/File:Ruby_transmittance.svghttp://en.wikipedia.org/wiki/File:Ruby_laser_rod_and_view_through.JPGhttp://en.wikipedia.org/wiki/File:Ruby_laser_rod_and_view_through.JPGhttp://en.wikipedia.org/wiki/Laser_pumpinghttp://en.wikipedia.org/wiki/Flashtubehttp://en.wikipedia.org/wiki/Population_inversionhttp://en.wikipedia.org/wiki/Optical_cavityhttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Stimulated_emissionhttp://en.wikipedia.org/wiki/Population_inversion#Three-level_lasershttp://en.wikipedia.org/wiki/Active_laser_mediumhttp://en.wikipedia.org/wiki/Amplifierhttp://en.wikipedia.org/wiki/Synthetic_rubyhttp://en.wikipedia.org/wiki/Optical_pumpinghttp://en.wikipedia.org/wiki/Optical_pumpinghttp://en.wikipedia.org/wiki/Xenonhttp://en.wikipedia.org/wiki/Silveringhttp://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_etalonhttp://en.wikipedia.org/wiki/Gires-Tournois_etalonhttp://en.wikipedia.org/wiki/Antireflection_coatinghttp://en.wikipedia.org/wiki/Brewster's_anglehttp://en.wikipedia.org/wiki/Dielectric_mirrorhttp://en.wikipedia.org/wiki/Curved_mirror


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Transmittance of ruy in o#tical and near/I6 s#ectra! =ote the two road lue and"reen asor#tion ands and the narrow asor#tion and at 7% nm, which is thewavelen"th of the ruy laser!6uy also asors some of the li"ht at its lasin" wavelen"th! To overcome thisasor#tion, the entire len"th of the rod needs to e #um#ed, leavin" no shaded areas

near the mountin"s! The active #art of the ruy is the do#ant, which consists ofchromiumions sus#ended in a sa##hirecrystal! The do#ant often com#rises around8!8+Z of the crystal, and is res#onsile for all of the asor#tion and emission ofradiation!


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written a #a#er on ruy fluorescence, felt that Schawlow was ein" *too #essimistic!*His measurements indicated that the lowest ener"y level of #in) ruy could at least e

#artially de#leted y #um#in" with a very intense li"ht source, and, since ruy wasreadily availale, he decided to try it anyway!Also attendin" the conference was Gordon Gould! Gould su""ested that, y #ulsin"

the laser, #ea) out#uts as hi"h as a me"awatt could e #roduced!

Com#onents of ori"inal ruy laser

As time went on, many scientists e"an to dout the usefulness of ruy as a lasermedium! Maiman, too, felt his own douts, ut, ein" a very *sin"le/minded #erson,*he )e#t wor)in" on his #ro@ect in secret! He searched to find a li"ht source that would

e intense enou"h to #um# the rod, and an elli#tical #um#in" cavity of hi"hreflectivity, to direct the ener"y into the rod! He found his li"ht source when asalesman from General 'lectric showed him a few ;enonflashtues,claimin" that thelar"est could i"nite steel wool if #laced near the tue! Maiman reali(ed that, with suchintensity, he did not need such a hi"hly reflective #um#in" cavity, and, with thehelical lam#, would not need it to have an elli#tical sha#e! Maiman constructed hisruy laser at the Hu"hs 6esearch Laoratory, in Maliu California! He used a #in)ruy rod, measurin" $ cm y $!+ cm, and, on May $7, $%78, fired the device,

#roducin" the first eam of laser li"ht!Theodore Maimans ori"inal ruy laser is still o#erational! It was demonstrated onMay $+, 18$8 at a sym#osium co/hosted in ancouver, British Columiay the


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Model Eour: Lasers0NTR;%T0NThe word *laser* is an acronym for Li"ht Am#lification y Stimulated 'mission of6adiation! Lasers are findin" ever increasin" military a##lications // #rinci#ally fortar"et ac4uisition, fire control, and trainin"! These lasers are termed ran"efinders,tar"et desi"nators, and direct/fire simulators! Lasers are also ein" used in
http://www.fas.org/man/dod-101/navy/docs/laser/fundamentals_glossary.htmhttp://www.fas.org/man/dod-101/navy/docs/laser/fundamentals_glossary.htm


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communications, laser radars -LI


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The color of li"ht is determined y its fre4uency or wavelen"th! The shorterwavelen"ths are the ultraviolet and the lon"er wavelen"ths are the infrared! Thesmallest #article of li"ht ener"y is descried y 4uantum mechanics as a #hoton! The

ener"y, ', of a #hoton is determined y its fre4uency, , and >lanc)s constant, h!

-$.

The velocity of li"ht in a vacuum, c, is 88 million meters #er second! The

wavelen"th, , of li"ht is related to from the followin" e4uation:

-1.

The difference in ener"y levels across which an e;cited electron dro#s determines thewavelen"th of the emitted li"ht!

Figure 2. Emission of radiation from an atom by transition of an

electron from a higher energy state to a lower energy state

%PNENTS 8 A LASER

As shown in fi"ure , the three asic com#onents of a laser are:Lasin" material -crystal, "as, semiconductor, dye, etc!!!.>um# source -adds ener"y to the lasin" material , e!"! flash lam#, electrical current tocause electron collisions, radiation from a laser, etc!.0#tical cavity consistin" of reflectors to act as the feedac) mechanism for li"htam#lification

Figure 3. Solid State Laser Diagram

'lectrons in the atoms of the lasin" material normally reside in a steady/state lowerener"y level! 5hen li"ht ener"y from the flashlam# is added to the atoms of the lasin"material, the ma@ority of the electrons are e;cited to a hi"her ener"y level // a

#henomenon )nown as #o#ulation inversion! This is an unstale condition for theseelectrons! They will stay in this state for a short time and then decay ac) to theirori"inal ener"y state! This decay occurs in two ways: s#ontaneous decay // the


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electrons sim#ly fall to their "round state while emittin" randomly directed #hotonsand stimulated decay // the #hotons from s#ontaneous decayin" electrons stri)e othere;cited electrons which causes them to fall to their "round state! This stimulatedtransition will release ener"y in the form of #hotons of li"ht that travel in #hase at thesame wavelen"th and in the same direction as the incident #hoton! If the direction is

#arallel to the o#tical a;is, the emitted #hotons travel ac) and forth in the o#ticalcavity throu"h the lasin" material etween the totally reflectin" mirror and the

#artially reflectin" mirror! The li"ht ener"y is am#lified in this manner until sufficientener"y is uilt u# for a urst of laser li"ht to e transmitted throu"h the #artiallyreflectin" mirror!As shown in fi"ure , a lasin" medium must have at least one e;cited -metastale.state where electrons can e tra##ed lon" enou"h -microseconds to milliseconds. for a

#o#ulation inversion to occur! Althou"h laser action is #ossile with only two ener"ylevels, most lasers have four or more levels!

Figure 4. hree le!el laser energy diagram

A J/switch in the o#tical #ath is a method of #rovidin" laser #ulses of an e;tremelyshort time duration! A rotatin" #rism li)e the total reflector in fi"ure was an earlymethod of #rovidin" J/switchin"! 0nly at the #oint of rotation when there is a clearo#tical #ath will li"ht ener"y e allowed to #ass! A normally o#a4ue electro/o#ticaldevice -e!"!, a #oc)els cell. is now often used for a J/switchin" device! At the time ofvolta"e a##lication, the device ecomes trans#arent, the li"ht uilt u# in the cavity ye;cited atoms can then reach the mirror so that the cavity Juality, J, increases to a

hi"h level and emits a hi"h #ea) #ower laser #ulse of a few nanoseconds duration!5hen the #hases of different fre4uency modes of a laser are synchroni(ed -loc)edto"ether., these modes will interfere with each other and "enerate a eat effect! Theresult is a laser out#ut with re"ularly s#aced #ulsations called *mode loc)in"*! Modeloc)ed lasers usually #roduce trains of #ulses with a duration of a few #icoseconds tonanoseconds resultin" in hi"her #ea) #owers than the same laser o#eratin" in the J/switched mode! >ulsed lasers are often desi"ned to #roduce re#etitive #ulses! The

#ulse re#etition fre4uency, #rf, as well as #ulse width is e;tremely im#ortant inevaluatin" iolo"ical effects!

T2PES 8 LASERS


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The laser diode is a li"ht emittin" diode with an o#tical cavity to am#lify the li"htemitted from the ener"y and "a# that e;ists in semiconductors as shown in fi"ure +!They can e tuned y varyin" the a##lied current, tem#erature or ma"netic field!

Figure ". Semiconductor laser diagram

Gas lasers consist of a "as filled tue #laced in the laser cavity as shown in fi"ure 7! Avolta"e -the e;ternal #um# source. is a##lied to the tue to e;cite the atoms in the "as

to a #o#ulation inversion! The li"ht emitted from this ty#e of laser is normallycontinuous wave -C5.! 0ne should note that if rewster an"le windows are attachedto the "as dischar"e tue, some laser radiation may e reflected out the side of thelaser cavity! Lar"e "as lasers )nown as "as dynamic lasers use a comustion chamerand su#ersonic no((le for #o#ulation inversion!

Figure #. $as laser diagram

Ei"ure & shows a dye laser dia"ram!


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Figure '. Free Electron Laser Diagram

Laser eam "eometries dis#lay transverse electroma"netic -T'M. wave #atternsacross the eam similar to microwaves in a wave "uide! Ei"ure % shows somecommon T'M modes in a cross section of a laser eam!

Figure ( &ommon E) laser beam modes

A laser o#eratin" in the mode could e considered as two lasers o#eratin" side

y side! The ideal mode for most laser a##lications is the mode and this modeis normally assumed to easily #erform laser ha(ards analysis! Li"ht from aconventional li"ht source is e;tremely roadand -containin" wavelen"ths across theelectroma"netic s#ectrum.! If one were to #lace a filter that would allow only a verynarrow and of wavelen"ths in front of a white or roadand li"ht source, only asin"le li"ht color would e seen e;itin" the filter! Li"ht from the laser is similar to theli"ht seen from the filter! However, instead of a narrow and of wavelen"ths none ofwhich is dominant as in the case of the filter, there is a much narrower linewidthaout a dominant center fre4uency emitted from the laser! The color or wavelen"th ofli"ht ein" emitted de#ends on the ty#e of lasin" material ein" used! Eor e;am#le, ifa =eodymium:Dttrium Aluminum Garnet -=d:DAG. crystal is used as the lasin"material, li"ht with a wavelen"th of $87 nm will e emitted! Tale $ illustratesvarious ty#es of material currently used for lasin" and the wavelen"ths that areemitted y that ty#e of laser! =ote that certain materials and "ases are ca#ale ofemittin" more than one wavelen"th! The wavelen"th of the li"ht emitted in this case isde#endent on the o#tical confi"uration of the laser!able 1. &ommon Lasers and heir *a!elengths

LASER T2PE

3A


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Helium =eon +, +%, 7$1, and 71!2

Fry#ton&!+ / &%%! -7&!$ / 7&7!most used.

6uy 7%!

Laser


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Figure 11. Di!ergence of Laser Source

Eor e;am#le, a laser ca#ale of deliverin" a $88 m #ulse in 18 ns has a #ea) #owerof + million watts! A C5 laser will usually have the li"ht ener"y e;#ressed in watts,

and a #ulsed laser will usually have its out#ut e;#ressed in @oules! Since ener"ycannot e created or destroyed, the amount of ener"y availale in a vacuum at theout#ut of the laser will e the same amount of ener"y contained within the eam atsome #oint downran"e -with some loss in the atmos#here.! Ei"ure $1 illustrates aty#ical laser eam! The amount of ener"y availale within the sam#lin" area will econsideraly less than the amount of ener"y availale within the eam! Eor e;am#le,

a $88 m5 laser out#ut mi"ht have 8 m5 measured within $ sam#le area! The

irradiance in this e;am#le is 8 m53 !

Figure 12. ,llustration of ,rradiance

%/ARA%TER0ST0%S 8 ATER0ALSMaterials can reflect, asor, and3or transmit li"ht rays! 6eflection of li"ht is estillustrated y a mirror! If li"ht rays stri)e a mirror, almost all of the ener"y incident onthe mirror will e reflected! Ei"ure $ illustrates how a #lastic or "lass surface will acton an incident li"ht ray! The sum of ener"y transmitted, asored, and reflected wille4ual the amount of ener"y incident u#on the surface!A surface is s#ecular -mirror/li)e. if the si(e of surface im#erfections and variationsare much smaller than the wavelen"th of incident o#tical radiation! 5henirre"ularities are randomly oriented and are much lar"er than the wavelen"th, then thesurface is considered diffuse! In the intermediate re"ion, it is sometimes necessary tore"ard the diffuse and s#ecular com#onents se#arately!


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Figure 13. Light -ay ,ncident to $lass Surface

A flat s#ecular surface will not chan"e the diver"ence of the incident li"ht eamsi"nificantly! However, curved s#ecular surfaces may chan"e the diver"ence! Theamount that the diver"ence is chan"ed is de#endent on the curvature of the surface!Ei"ure $ demonstrates these two ty#es of surfaces and how they will reflect anincident laser eam! The diver"ence and the curvature of the reflector have eene;a""erated to etter illustrate the effects! =ote that the value of irradiance measuredat a s#ecific ran"e from the reflector will e less after reflection from the curvedsurface than when reflected from the flat surface unless the curved reflector focuses

the eam near or at that ran"e!A diffuse surface is a surface that will reflect the incident laser eam in all directions!The eam #ath is not maintained when the laser eam stri)es a diffuse reflector!5hether a surface is a diffuse reflector or a s#ecular reflector will de#end u#on thewavelen"th of the incident laser eam! A surface that would e a diffuse reflector fora visile laser eam mi"ht e a s#ecular reflector for an infrared laser eam -e!"!,

.! As illustrated in Ei"ure $+, the effect of various curvatures of diffuse reflectorsma)es little difference on the reflected eam!If li"ht is incident u#on an interface se#aratin" two transmittin" media -as an air/"lassinterface., some li"ht will e transmitted while some will e reflected from thesurface! If no ener"y is asored at the interface, T [ 6 U $ where T and 6 are thefractions of the incident eam intensity that are transmitted and reflected! T and 6 arecalled the transmission and reflection coefficients, res#ectively! These coefficientsde#end not only u#on the #ro#erties of the material and the wavelen"th of theradiation, ut also u#on the an"le of incidence! The amount of the incident li"ht eamthat is reflected and the amount transmitted throu"h the material is further de#endenton the #olari(ation of the li"ht eam!The an"le that an incident ray of radiation forms with the normal to the surface willdetermine the an"le of refraction and the an"le of reflection -the an"le of reflection

e4uals the an"le of incidence.! The relationshi# etween the an"le of incidence - .

and the an"le of refraction - . is

-.


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where n and n are the indices of refraction of the media that the incident andtransmitted rays move throu"h, res#ectively -see fi"ure $.!

Figure 14. Specular -eflectors

Figure 1". Diffuse -eflectors

Research for Lasers

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