Relatedtheories
Alllight(ietraditionallightsourceorlaserlightsource)iscausedbychangesintheenergylevelsofatomsandmolecules.Theabsorptionandreleaseofthesespecificenergyleveldifferencesappearaslightofspecificwavelengths.Theenergy(Joule)emittedbythephotonisequaltoh*f,wherehisthePlanckconstantandfisthefrequencyofradiation,whichissuitableforlasersandtraditionallight-emittingsystems.Lightradiationenergyisreleasedwhenatomsfallfromahighenergystatetoalowenergystate.However,ifanatomwantstoemitlight,itmustfirstabsorbtheenergy,sothatthelow-energystateatomishittoahigh-energystate,whichiscalled"pumping"inthelaserfield.Alllightincludingspontaneousandlaserrequiresacertainamountofenergyabsorption.
Obviously,nospontaneousemissionsourcecanreachthespectralqualityofalasersource.Thisisbecausethetraditionallightsourceisamessyradiationstatethatthesystemhasatvariousenergylevels.Thebasiccharacteristicsoftraditionallightsourcesarebroadspectraldistribution,randompolarization,circularandirregularwavefrontsandlowcolortemperature.Theemissionprincipleoflaserisdifferentfromconventionallight.Itisnotcausedbyspontaneousemissionofvariousenergylevels,butstimulatedemission.Atomsofvariousenergylevelsarepumpedtoahigherexcitedstate.Thetimeisgenerallydistributednormally.Mostoftheatomsfalltothesamelowerenergystateinaveryshortperiodoftime.Thisemissionmethodcausesthelighttobeatalmostthesameenergylevel,whichiswhatweusuallycalllaser.Monochromaticity.
Inordertomaintainthenumberofflippedparticlesenough,theremustbeexternalenergytomovethefallenatomstotheexcitedstate,whichrequirespulsesinpulsedlasers(suchasYAGlasers,rubylasers)Xenonlamps,semiconductorlasersindiodepumpedlasers(alsocalledDPSSlasers,suchasgreenlaserpointers),gasdischargelasers(suchashelium-neonlasers,CO2lasers),chemicallasers(suchasweapon-gradeoxygen-iodinelasers)Thechemicalreactionintheenergysourceprovidesenergy.
Manysubstancesintheworldcanbeexcitedbylight,butonlyafewsubstancescanemitusefullaserlight.Thelasersubstancemusthaveaspecificparticlestructuresothattheparticleinversiongroupcanbeexcitedtoacertaindensity,usuallysomecrystals,gases,orliquids.Theselasermaterialsaregenerallyplacedbetweentwomirrors,sothattheenergycanbeamplifiedtoausablelevelthroughmultiplereflectionsbackandforth.Amirrorisatotalmirror,whichreflectsalmostalllight,alsocalledHR,andtheotherisahalfmirror,alsocalledanoutputmirror,OC,whichgenerallyreflects20%to80%ofthelight.Thelaserisrepeatedlybetweenthetwomirrors.Afterzoomingbackandforth,apartofitistypedoutforoutput.
Shortlyafterthelaserideawasputforward,rubywasfirstusedtomaketheworld'sfirstlaser.ThematrixoftherubycrystalforlaserisAl2O3,andthecrystalisdopedwithabout0.05%(weightratio)Cr2O3.ThedensityofCr3+isabout1.58×1019/cm3.Cr3+replacesthepositionofAl3+inthecrystalandisevenlydistributedinthecrystal.Optically,itbelongstoanegativeuniaxialcrystal.UndertheirradiationoftheXe(xenon)lamp,theparticlesintherubycrystaloriginallyinthegroundstateE1absorbthephotonsemittedbytheXelampandareexcitedtotheE3level.TheaveragelifetimeofparticlesattheE3energylevelisveryshort(about10-9seconds).MostparticlesreachtheupperenergylevelE2ofthelaserthroughnon-radiativetransitions.ThelifespanofparticlesattheE2energylevelisverylong,upto3×10-3seconds.Therefore,alargenumberofparticlesaccumulateattheE2energylevel,formingapopulationinversionbetweenE2andE1.Atthistime,thecrystalpairfrequencyνsatisfieshν=E2—E1(wherehisPlanck'sconstant,E2andE1arelaserThephotonsoftheenergyoftheupperandlowerenergylevelshaveamplifyingeffect,thatis,thereisagaintothelightofthisfrequency.WhenthegainGislargeenoughtomeetthethresholdcondition,thereisalaseroutputwithawavelengthof6943×10-10mattheendofthepartialreflector.
Morethanhalfoftheatomsinthe4Aenergylevel(lowenergystate)inthesystemarepumpedtoahigherenergystatebyexternalenergy,andthelasercanbereleased.ItcanbeseenfromFigure2thatmostoftheabsorptionofrubylaserisconcentratedintworegions,T1(ultraviolet)andT2(greenlight).Thespectralwidthoftheseregionswheretheefficiencyoftheabsorptionbandisrelativelyhighisabout1000A.TheionshittotheT1/T2statequicklyfalltothe2Eenergylevel,causingthedensityofthe2Eflipgrouptoincreasetothethresholdvalueforlasershots.Belowthisthresholddensity,rubycanneitheremitlaserlight,norcanitbeusedtoamplifylaserlight(infact,thetwoarethesameprinciple).Afterthat,whentheenergystateisfrom2Etothelowenergystate,theextraenergyisemittedintheformoflightwithawavelengthof6943A.The6943lightemittedwhena2Eenergylevelionfallstoalowenergystatepromptsthesurrounding2Etoalsofollowit,whichcanbeunderstoodasachainreactionwitharelativelylowsuccessrate.ThispictureisanextremelysimplifiedpictureThispictureisanextremelysimplifiedandinaccuratenon-scalemodel.Itisanon-scale,inaccurateandnon-scalemodel.Itdoesnotshowsomeofthefineenergylevelsinthe2E/4Aenergylevel.Irememberthat2EChineseseemstobecalledmetastablestate.YoucanGoogleforspecificdetails.Thesefineenergylevelswillmixthe6943Alaserintosomenearbypeaks.Thisquestiondoesnotaffectgeneralexperiments.Ifyouneedaparticularlypurespectrum,youcancoolthelaserrodtoabout75K,atthistimethelinewidthwillbecomeabout10-15GHznarrow.
Althoughtheefficiencyofrubylaserisnothigh,only0.1%,itproducesdarkred694.3nmlight,butbecauseitsstructureisextremelysimpleandrepresentative,itisthemostwidelyusedYAGlaserstructure.Consistent,theenergylevels(three-levelsystem)aresimplerandeasiertounderstandinanalysis.Thepencoreisthickandthin,andtherubyrodaslongasthefingercaneasilygeneratethedetectedlaserbeamthatpenetratestheironsheetandisreflectedfromthelunarsurface.TheselasershavenotinventedthemuchmoreefficientYAGlaserrod(1%-3%),itiswidelyusedinlasercuttingmachinesanddrillingmachines,andmanymilitarynon-lethalweaponsalsousesmallerrubysticks.
RubyLaserAtlas(1sheet)
RubyLaserAtlas(1photo)
Rubyisathree-levellasermaterial.Generally,thealuminumoxidecrystalwithgoodopticalperformanceismixedwith0.03-0.4%Cr3+,madeintoartificialrubies,hasmuchbetteropticalpropertiesthanordinarynaturalrubies.Commonrubyrodsrangeinsizefrom0.5cmto2cmindiameterand4cmto16cminlength.Itmaylooklikeaverylightpinkglassrodoraverydarkreddishbrown,dependingontheCrdopedconcentrationoftherod.Whenyouhititwithagreenlaserpointer,averyspecialcolorwillcomeout.
Althoughthestructureisextremelysimple,itisstillacommonhigh-energypulsedlaser.Itisasolid-statelaserequivalenttoYAGlaserandneodymiumglasslaser.Theworkingefficiencyofrubylaserunderpulsedxenonlampirradiationisonlyabout0.1%,butduetothelongfluorescentlifetime,mechanicalQ-switching(arotatingall-reflectionprismtocompressthepulsetotheorderofnsiseasy,andthepulsepowercaneasilyexceedtrillions.watt).
HereisabriefexplanationoftheQswitch.ThesimplestQ-switchisamotorconnectedtoamirror.Whenitisnotaligned,thereisnobackandforthlight,whichcanallowthenumberofhigh-energyparticlestograduallyaccumulateandincrease.Theyarereleasedatthemomentofalignment,reachingaverynarrowandhighpower.Bigpulse.AnothertypeofQ-switchsuitableforDIYisthepassiveq-switch.Whenthelightenergydensityreachesacertainthreshold,itsuddenlychangesfromnotverytransparenttoverytransparent,causingthepreviouslygatheredhigh-energyparticlesCanbereleasedinstantly,thiskindofcrystalismoredifficulttofind,andthepriceisrelativelyhigh,youcanonlytakeluck.Theq-switchesusedintheindustryareelectro-opticQ-switching,acousto-opticQ-switching,etc.,whichareusedtofurthercompressthepulsesofpulsedlasersortomakecontinuoussemiconductor-pumpedlasercrystalsoutputpulsedlaserswithhighpeakpower,whichisconvenientMarkingandcutting.
Birthbackground
TheconceptofstimulatedemissionproposedbyEinsteinisitsimportanttheoreticalbasis.Thistheorystatesthatamaterialparticleinahigh-energystatewillbeconvertedtoalow-energystatebyaphotonwhoseenergyisequaltotheenergydifferencebetweenthetwoenergylevels,andasecondphotonwillbeproduced,whichisemittedatthesametimeasthefirstphoton.Thisisstimulatedemission.Thelightoutputbythisradiationisamplifiedandiscoherentlight,thatis,theemissiondirection,frequency,phase,andpolarizationofmultiplephotonsareexactlythesame.
Sincethen,theestablishmentanddevelopmentofquantummechanicshasenabledpeopletohaveadeeperunderstandingofthemicrostructureandmotionlawsofmatter,andtheenergyleveldistribution,transitionandphotonradiationofmicroscopicparticleshavealsobecomemorepowerful.ThisprovesthatthisalsoobjectivelyperfectsEinstein’sstimulatedemissiontheoryandfurtherlaysatheoreticalfoundationfortheproductionoflasers.Afterthebirthofquantumelectronicsinthelate1940s,itwasquicklyappliedtostudytheinteractionbetweenelectromagneticradiationandvariousmicroscopicparticlesystems,andmanycorrespondingdevicesweredeveloped.Therapiddevelopmentofthesescientifictheoriesandtechnologieshavecreatedconditionsfortheinventionoflasers.
In1951,AmericanphysicistsPurcellandPoundsucceededincausingapopulationinversioninanexperiment,andobtained50kilohertzpersecondstimulatedradiation.Later,AmericanphysicistCharlesTownsandSovietphysicistsMasovandProkhorovsuccessivelyproposeddesignsthatusetheprincipleofstimulatedemissionofatomsandmoleculestogenerateandamplifymicrowaves.
In1960,theAmericanphysicistTheodorMaymanbarelywonthisworldwidedevelopmentcompetitioninhisresearchlaboratoryinMiami,Florida.Heusedahigh-strengthflashtubetostimulatethechromiumatomsintherubycrystal,therebyproducingafairlyconcentratedslenderredbeamoflight,whichwhenitisshotatacertainpoint,canmakethispointreachatemperaturehigherthanthesun.
Inventor
TheAmericanphysicistandinventoroftheworld’sfirstlaser,TheodoreH.Maiman,fellillinBritishColumbia,Vancouver,Canada.Theuniversitypassedawayattheageof79.Maymansufferedfromsystemicmastocytosis,araregeneticdisease.
Throughouthislife,Maymanreceivednumerousrewards.AlthoughtheNobelPrizeinPhysicsin1964wasnotawardedtohimwhoinventedtheworld’sfirstlaser,itwasgiventotheAmericanBellLaboratoryphysicistTang,whoinventedthemaserandproposedtheprincipleanddesignofthelaser.SriLankaandtheSovietphysicistsBasovandProkhorov,butMemanwasnominatedfortheNobelPrizetwice,andwonthefamousJapanesePrizeandWolfPrizeinthefieldofphysics.Hewasalsoincludedinthe"NationalInventorsHallofFame"(NationalInventorsHallofFame)in1984.Inabookdedicatedtothe100thanniversaryofNature,TownsreferredtoMayman'spaperas"themostimportantoneofallthewonderfulpaperspublishedinthemagazineoverthepast100years."
TheeventtocommemorateMaymanisheldonMay16theachyear,whichisalsothedaywhenMayman’slasersareusedforthefirsttime.
Inventionprocess
Thelasergeneratesakindofcoherentopticalradiation(laser)throughtheprincipleofstimulatedemissionamplification.OnJuly7,1960,the"NewYorkTimes"firstdisclosedthatMaymanhadsuccessfullymadetheworld'sfirstrubylaser.Heirradiatedaspecialrubycrystalthesizeofafingerwiththelightofaflashtocreateacoherentpulse.Laserbeam,thisresultlatershockedtheworld.Withtheworld'stoplaboratoriesfightingforthefirstlaserinvention,Mayman'semployeratthetime,theHughesAircraftCompanyinLosAngeles(HughesAircraftCompany)won.
However,Maymandidnotgowellwhenpublishingthearticle.Hefirstsubmittedthepapertothe"PhysicalReviewLetters"(PRL),butthetheneditorSamGoudsmitbelievedthatthiswasjustanothermaser'srepetitivework,soherefusedtopublishit.LaterMaymanfinallypublishedthearticleinthejournalNature.Ofcourse,afteryearsofhardwork,Mayman'sachievementshavebeenwidelyrecognized.
MaymanwasborninLosAngeles,CaliforniaonJuly11,1927,thesonofanelectricalengineer.Hisfatherwantedhimtobecomeadoctor,buthebelievedthatthestudyoflaserswouldhaveagreaterimpactonmedicine.AlthoughMaymanwasawildchildwhenhewasachild,hewasverygoodatmath.AftergraduatingfromtheUniversityofColoradowithamaster'sdegreein1949,MaymancametoStanfordUniversitytostudyforadoctoraldegree,andreceivedhisdoctoratein1955.HissupervisorwasWillisE.Lamb,whowontheNobelPrizeinPhysicsin1955..
WhileworkingatHughesAircraftCompany,Maymantoldhisbossthathehopedtomakealaser,butsinceotherfamouslaboratoriesdidnotproduceanyexcitingresultsatthetime,HughesstillhopedHedoessome"useful"workonthecomputer.ButMaymaninsistedonconductingresearchandthreatenedtoresign.Intheend,thecompanygavehim9months,50,000USdollarsandanassistant.
Afterthesuccessofthefirstlaser,Maymancontinuedtostudytheapplicationoflasersinmedicaltreatment,althoughthepublicatthetimebelievedthatitwasa"lethal"light.However,becauseHughesdidnotinvestmoreinthepotentialapplicationsoflasers,MaymanchosetoleaveandfoundedhisownKoradcompanyin1961.
Application
Mayman’sinventionhasmadeasignificantcontributiontomankind.Lasershavebecomeindispensablebasicequipmentinmedicine,industry,andmanyscientificresearchfields.Forexample,intheapplicationofjadeprocessing,theapplicationofholographicphotos,etc.
Technologydevelopment
Obviously,theprerequisiteforlasergenerationisthatastrongbeamofultravioletandgreenlightisirradiatedintothelaserrod,sothattheionturnoverdensityreachesthethreshold.Awidelyusedmethodistouseapulsedxenonlampasastronglightsource.Thestructureisverysimple,justprojectthelightofthexenonlampontotherubyrod.
Hereisanintroductiontotheflash.
Flash,thereareseveralimportantparameters.Weareactuallyconcernedabouttwo,arclengthand1800v,theenergyofthelampundertheelectrolyticcapacitor.Ingeneral,inordertoadapttoindustrialuse,thenominalworkingvoltageofthedatasheetisavalueabove1500v.Onlybymeetingthisenergystoragevoltagecanthenominallightenergydensityandpulsewidthbeachieved(themainpeakisbelow0.5ms,whichcanmeettheneedsofpunching.).
Therearetwomainstreamflashes:
Ringflash
Theworld’sfirstlaserusedamultiRingflashlight.Theefficiencyisnotashighasthatofalinearflashlamp,buttheenergytoleranceismuchgreater.Thiskindofflashisgenerallydifficulttobuy,becausethetubelengthistoolargetotrigger,thepulseshapingnetworkisdifficulttomake,andthecapacitorenergystoragevoltageishigh,butitissuitableforaflashthatcanwithstandverylargeenergy.Thiskindofflashlightmodelingisdifficult,thedatasheetdataisverydifferent,thereisnogeneralruleofsummary.Thegeneralworkwithstandenergyexceeds2KJ.
Linearflashlamp
Today,morethan80%ofindustrialsolid-statelasersusethisxenonlampstructure.Highpumpingefficiency,convenientuseofwatercooling,simplemanufacturingprocess,andeasytriggeringarethereasonswhymostindustriallasersadoptthisstructure.Theseflashlampsarepulsedxenonlamps.Atypicalvalueisthataxenonlampwith10cmarclengthand8mmdiametercaneasilyhold2200Jofenergyunder400Venergystorage.