Laser

Historicaldevelopment

TheEnglishwordlaserisderivedfromtheinitialacronymLASER,whichmeans"stimulatedemissionopticalamplifier"inEnglish.Theabbreviationisabbreviated.

Thekeyconceptinlasertechnologyhasbeenestablishedasearlyas1917whenEinsteinproposed"stimulatedemission".Thetermlaserwasoncecontroversial;GordonGouldwasthefirsttouseitintherecordPeoplewiththisvocabulary.

In1953,AmericanphysicistCharlesHardeTownsandhisstudentArthurXiaoLuomadethefirstmicrowavequantumamplifierandobtainedahighlycoherentmicrowavebeam.

In1958,C.H.TownsandA.L.XiaoLuoextendedtheprincipleofmicrowavequantumamplifierstotheopticalfrequencyrange.

In1960,T.H.TheodoreMaymanmadethefirstruby​​laser.

In1961,IranianscientistA.Jiawenandothersmadeahelium-neonlaser.

In1962,R.N.Hallandotherscreatedagalliumarsenidesemiconductorlaser.

In2013,researchersfromtheNationalLaserCenteroftheSouthAfricanScienceandIndustryResearchCouncildevelopedtheworld'sfirstdigitallaser,openingupnewprospectsforlaserapplications.TheresearchresultswerepublishedintheBritishjournalNatureCommunicationsonAugust2,2013.

Thedisputeoverlaserpatents

ThelaserwasfirstbuiltbyscientistGordonGouldin1958,butdidnotpublishrelatedpapersuntil1959,butwasRejected,becausehismentorwasCharlesTownes,theinventorofthemaser(microwaveresonator)technology(inventedthetechnologytogeneratemicrowaveoutput).Duetotheinfluenceofthetutor,thepatenthasnotbeenapproved.ThepatentforthelaserwasnotapprovedintheUnitedStatesuntil1977.

Thelong-termpatentwarismorebeneficialtoGould,becausewhenheobtainedthepatent,thelaserhadbeenusedonalargescale,andthepatentprotectionperiodwaslimited.Ifthepatentwasapprovedassoonastheapplicationwasfiled,becauseIt’snotwidelyused,butitwon’tmakemuchmoney.

Typesandusesoflasers

Thepurequalityandstablespectrumoflaserlightcanbeusedinmanyways.

Rubylaser:Theoriginallaserwasthatruby​​wasexcitedbyabrightflashingbulb,andthelaserproducedwasa"pulselaser"ratherthanacontinuousandstablebeam.Thequalityofthebeamproducedbythislaserisfundamentallydifferentfromthelaserproducedbythelaserdiodeweareusingnow.Thisintenselightemissionthatlastsonlyafewnanosecondsisverysuitableforcapturingeasilymovingobjects,suchasholographicportraitsofpeople.Thefirstlaserportraitwasbornin1967.Rubylasersrequireexpensiverubiesandcanonlyproduceshortpulsesoflight.

HeNelaser:In1960,scientistsAliJavan,WilliamR.BrennetJr.andDonaldHerriotdesignedaHeNelaser.Thisisthefirstgaslaser,whichiscommonlyusedbyholographicphotographers.Twoadvantages:1.Producecontinuouslaseroutput;2.Donotneedflashbulbforlightexcitation,butuseelectricexcitationgas.

Laserdiode:Laserdiodeisoneofthemostcommonlyusedlasers.ThephenomenonofspontaneousrecombinationofelectronsandholesonbothsidesofthePNjunctionofthediodetoemitlightiscalledspontaneousemission.Whenthephotongeneratedbyspontaneousradiationpassesthroughthesemiconductor,onceitpassesthevicinityoftheemittedelectron-holepair,itcanexcitethetwotorecombineandproducenewphotons.Thisphotoninducestheexcitedcarrierstorecombineandemitnewphotons.Thephenomenoniscalledstimulatedemission.Iftheinjectedcurrentislargeenough,thecarrierdistributionoppositetothethermalequilibriumstatewillbeformed,thatis,thepopulationinversion.Whenthecarriersintheactivelayerareinalargenumberofinversions,asmallamountofspontaneousradiationgeneratedphotonsgenerateinducedradiationduetothereciprocatingreflectionatbothendsoftheresonantcavity,resultinginfrequency-selectiveresonantpositivefeedback,orgainingacertainfrequency.Whenthegainisgreaterthantheabsorptionloss,acoherentlightwithgoodspectrallines-laserlightcanbeemittedfromthePNjunction.Theinventionofthelaserdiodeallowslaserapplicationstoberapidlypopularized.Varioustypesofinformationscanning,opticalfibercommunications,laserranging,lidar,laserdiscs,laserpointers,supermarketcollections,etc.,areconstantlybeingdevelopedandpopularized.

Principle

Exceptforfreeelectronlasers,thebasicworkingprinciplesofvariouslasersarethesame.Theindispensableconditionsforlasergenerationarepopulationinversionandgaingreaterthanloss,sotheindispensablecomponentsinthedeviceareexcitation(orpumping)sourceandworkingmediumwithmetastableenergylevel.Excitationmeansthattheworkingmediumisexcitedtoanexcitedstateafterabsorbingexternalenergy,creatingconditionsforrealizingandmaintainingthepopulationinversion.Excitationmethodsincludeopticalexcitation,electricalexcitation,chemicalexcitationandnuclearenergyexcitation.Themetastableenergyleveloftheworkingmediummakesthestimulatedradiationdominate,therebyrealizingopticalamplification.Commoncomponentsinlasersincluderesonantcavity,butresonantcavity(seeopticalresonantcavity)isnotanindispensablecomponent.Theresonantcavitycanmakethephotonsinthecavityhavethesamefrequency,phaseanddirectionofoperation,sothatthelaserhasGooddirectionalityandcoherence.Moreover,itcanshortenthelengthoftheworkingmaterialwell,andcanalsoadjustthemodeofthelaserproducedbychangingthelengthoftheresonantcavity(iemodeselection),sogenerallylasershaveresonantcavities.

Laserworkingmaterial

referstothematerialsystemusedtorealizethepopulationinversionandthestimulatedradiationamplificationoflight,sometimescalledlasergainmedium,theycanbeMediumssuchassolids(crystals,glass),gases(atomicgas,ionicgas,moleculargas),semiconductorsandliquids.Themainrequirementforthelaserworkingsubstanceistoachieveagreaterdegreeofpopulationinversionbetweenthespecificenergylevelsofitsworkingparticlesasmuchaspossible,andtokeepthisinversionaseffectivelyaspossibleduringtheentirelaseremissionprocess;Forthisreason,theworkingsubstanceisrequiredtohavesuitableenergylevelstructureandtransitioncharacteristics.

Excitationpumpingsystem

referstoamechanismordevicethatprovidesanenergysourceforthelaserworkingsubstancetoachieveandmaintainthepopulationreversal.Dependingontheworkingmaterialandtheoperatingconditionsofthelaser,differentexcitationmethodsandexcitationdevicescanbeadopted,thefollowingfourcommonones.①Opticalexcitation(opticalpump).Thelightemittedbyanexternallightsourceisusedtoirradiatetheworkingsubstancetoachievethepopulationinversion.Theentireexcitationdeviceisusuallycomposedofagasdischargelightsource(suchasaxenonlamp,akryptonlamp)andacondenser.ThisexcitationmethodisalsocalledLamppumped.②Gasdischargeexcitation.Itusesthegasdischargeprocessthatoccursinthegasworkingsubstancetorealizethepopulationreversal.Theentireexcitationdeviceisusuallycomposedofadischargeelectrodeandadischargepowersupply.③Chemicalincentives.Itusesthechemicalreactionprocessthatoccursinsidetheworkingsubstancetoachievethepopulationreversal,whichusuallyrequiresappropriatechemicalreactantsandcorrespondinginitiationmeasures.④Nuclearenergyincentives.Itusesthefissionfragments,high-energyparticlesorradiationproducedbythesmallnuclearfissionreactiontoexcitetheworkingsubstanceandrealizethepopulationreversal.

Opticalresonantcavity

Usuallytwomirrorswithacertaingeometricshapeandopticalreflectioncharacteristicsarecombinedinaspecificway.Thefunctionis:①Provideopticalfeedbackcapability,sothatthestimulatedemissionphotonscangobackandforthinthecavitymanytimestoformacoherentcontinuousoscillation.②Limitthedirectionandfrequencyoftheoscillatingbeaminthecavitytoensurethattheoutputlaserhasacertaindirectionalityandmonochromaticity.Theeffectoftheresonantcavitydependsonthegeometryofthetwomirrors(radiusofcurvatureofthereflectingsurface)andtherelativecombinationofthetwomirrorsthatmakeupthecavity;Selectivelosscharacteristics).

Classification

Therearemanytypesoflasers.Below,wewillclassifyandintroducethelaserworkingmaterial,excitationmode,operationmode,outputwavelengthrangeandotheraspects.

Workingmaterial

Accordingtothestateoftheworkingmaterial,alllaserscanbedividedintothefollowingcategories:①Solid-statelasers(crystalandglass),whichareusedinthistypeoflaserTheworkingsubstanceismadebydopingthemetalionsthatcanproducestimulatedradiationintothecrystalorglassmatrixtoformtheluminouscenter;②Gaslasers,theworkingsubstancetheyuseisgas,andaccordingtotheactualproductioninthegasThenatureoftheworkingparticlesoftheexcitationeffectisdifferent,anditisfurtherdividedintoatomicgaslasers,iongaslasers,moleculargaslasers,excimergaslasers,etc.;③liquidlasers,theworkingmaterialsusedinthistypeoflasermainlyincludetwotypes,oneOneistheorganicfluorescentdyesolution,theotheristheinorganiccompoundsolutioncontainingrareearthmetalions,inwhichmetalions(suchasNd)playtheroleofworkingparticles,andtheinorganiccompoundliquid(suchasSeOCl2)playstheroleofthematrix;④semiconductorlasers,Thistypeoflaserusesacertainsemiconductormaterialasaworkingsubstancetoproducestimulatedemission.Itsprincipleistopassacertainexcitationmethod(electricinjection,opticalpumporhigh-energyelectronbeaminjection),betweenorbetweentheenergybandsofsemiconductormaterials.Betweentheenergyleveloftheimpurityandtheimpuritylevel,thepopulationinversionisrealizedbyexcitingtheunbalancedcarriers,therebygeneratingthestimulatedemissionoflight;⑤Freeelectronlaser,thisisaspecialtypeofnewlaser,theworkingsubstanceisinspaceThedirectionalfreeelectronbeammovingathighspeedinaperiodicmagneticfieldcangeneratetunablecoherentelectromagneticradiationaslongasthespeedofthefreeelectronbeamischanged.Inprinciple,itscoherentradiationspectrumcantransitionfromtheX-raybandtothemicrowaveregion,soitisveryattractiveProspects.

Gaslaser

Themediumisagaslaser,whichisexcitedbyelectricdischarge.

HeNelaser:themostimportantsourceofredlight(632.8nm).

Carbondioxidelaser:Thewavelengthisabout10.6μm(infrared),animportantindustriallaser.

Carbonmonoxidelaser:Thewavelengthisabout6-8μm(infrared),anditonlyworksundercoolingconditions.

Nitrogenlaser:337.1nm(ultraviolet).

Argonionlaser:withmultiplewavelengths,457.9nm(8%),476.5nm(12%),488.0nm(20%),496.5nm(12%),501.7nm(5%),514.5nm(43%)(frombluetogreen).

Helium-cadmiumlaser:themostimportantbluelight(442nm)andnear-ultravioletlasersource(325nm).

Kryptonionlaser:hasmultiplewavelengths,350.7nm,356.4nm,476.2nm,482.5nm,520.6nm,530.9nm,586.2nm,647.1nm(strongest),676.4nm,752.5nm,799.3nm(frombluelighttodeepredlight).

Oxygenionlaser

Xenonionlaser

Mixedgaslaser:doesnotcontainpuregas,butamixtureofseveralgases(generallyargon,krypton,etc.).

Excimerlaser:suchasKrF(248nm),XeF(351-353nm),ArF(193nm),XeCl(308nm),F2(157nm)(allUV).

Metalvaporlaser:Forexample,coppervaporlaser,thewavelengthisbetween510.6-578.2nm.Duetothegoodreinforcement,theresonatormirrorcanbeomitted.

Metalhalidelasers:suchascopperbromidelasers,withawavelengthbetween510.6-578.2nm.Duetothegoodreinforcement,theresonatormirrorcanbeomitted.

Chemicalexcitationlaserisaspecialform.Theexcitationiscarriedoutbyachemicalreactioninthemedium.Themediumisdisposableandisconsumedafteruse.Itisidealforhigh-powerconditionsandmilitaryfields.

Hydrochloricacidlaser

Iodinelaser

Solid-statelaser

Themediumisasolid-statelaser.Thiskindofworkingmaterialpassesthroughalamp,asemiconductorlaserarrayD.Otherlaserlightpumpsareexcited.Thethermallenseffectisadefectofmostsolid-statelasers.

Rubylaser:Theworld’sfirstlaser.OnJuly7,1960,AmericanyoungscientistMaymanannouncedthebirthoftheworld’sfirstlaser.Thislaserisaruby​​laser,anditsworkingwavelengthisgenerally6943,theworkingstateisasinglepulsetype,eachpulseisintheorderof1ms,andtheoutputenergyisintheorderofJoules.

Nd:YAG(neodymium-dopedyttriumaluminumgarnet):themostcommonlyusedsolid-statelaser,theworkingwavelengthisgenerally1064nm,thiswavelengthisafour-levelsystem,andthereareotherenergylevelsthatcanoutputotherwavelengthslaser.

Nd:YVO4(neodymium-dopedyttriumvanadate):themostwidelyusedsolid-statelaserwithlowpower.Theworkingwavelengthisgenerally1064nm.Itcangenerate532nmgreenlightafterfrequencymultiplicationbyKTPandLBOnonlinearcrystals..

Yb:YAG(ytterbium-dopedyttriumaluminumgarnet):suitableforhighpoweroutput,thedisclaserofthismaterialhasastrongadvantageinthefieldoflaserindustrialprocessing.

Titaniumsapphirelaser:hasawidewavelengthadjustmentrange(670nm～1200nm)

Semiconductorlaser

SemiconductorlaserAlsocalledItisasemiconductorlaserdiode,orlaserdiode(LaserDiode,LD)forshort.Duetothespecificityofthematerialstructureofthesemiconductormaterialandtheparticularityoftheelectronmovementlawinthesemiconductormaterial,theworkingcharacteristicsofthesemiconductorlaserhaveitsparticularity.

Semiconductorlasersaredevicesthatproducestimulatedemissionbyusingacertainsemiconductormaterialasaworkingsubstance.Theworkingprincipleistoachievenon-equilibriumloadingbetweentheenergybandofsemiconductormaterial(conductionbandandvalenceband)orbetweentheenergybandofsemiconductormaterialandtheenergylevelofimpurities(acceptorordonor)throughacertainexcitationmethod.Thenumberofcurrentparticlesisreversed.Whenalargenumberofelectronsandholesinthestateofnumberinversionrecombine,stimulatedemissionoccurs.Therearethreemainexcitationmethodsforsemiconductorlasers,namely,electricalinjection,opticalpumpingandhigh-energyelectronbeamexcitation.Electricalinjectionsemiconductorlasersaregenerallysemiconductorsurfacejunctiondiodesmadeofgalliumarsenide(GaAs),cadmiumsulfide(CdS),indiumphosphide(InP),zincsulfide(ZnS),etc.,andarebiasedintheforwarddirection.Voltageinjectioncurrentisusedforexcitation,andstimulatedemissionisgeneratedinthejunctionplanearea.Opticallypumpedsemiconductorlasers,generallyN-typeorP-typesemiconductorsinglecrystals(suchasGaAS,InAs,InSb,etc.)areusedasworkingmaterials,andlasersemittedbyotherlasersareusedasopticalpumps.High-energyelectronbeam-excitedsemiconductorlasersaregenerallyalsoUseN-typeorP-typesemiconductorsinglecrystals(suchasPbS,CdS,ZhO,etc.)astheworkingmaterial,whichisexcitedbyinjectinghigh-energyelectronbeamsfromtheoutside.Amongsemiconductorlaserdevices,theperformanceisbetterandthemostwidelyusedistheelectricinjectionGaAsdiodelaserwithdoubleheterostructure.

Semiconductorlasersarepumpedbyinjectioncurrent.

Thewavelengthcoverageofsemiconductorlasersisfromultraviolettoinfrared(300nmtomorethantenmicrons),ofwhich1.3umand1.55umaretwowindowsforopticalfibertransmission.Semiconductorlasershaveoutstandingcharacteristicssuchashighenergyconversionefficiency,easyhigh-speedcurrentmodulation,ultra-miniaturization,simplestructure,andlongservicelife,makingthemthemostimportantandmostvaluabletypeoflaser.

Semiconductorlasersareaclassoflasersthathavematuredanddevelopedrapidly.Becauseoftheirwidewavelengthrange,simpleproduction,lowcost,easymassproduction,andsmallsize,lightweight,andlonglife,Therefore,thevarietyisdevelopingrapidlyandtheapplicationrangeiswide.Therearemorethan300kindsofsemiconductorlasers.ThemostimportantapplicationfieldofsemiconductorlasersisGblocalareanetworks.Semiconductorlaserswithwavelengthsof850nmaresuitablefor1Gblocalareanetworks,andsemiconductorlaserswithwavelengthsof1300nm-1550nmaresuitablefor1OGblocalareanetworksystems.Theapplicationrangeofsemiconductorlaserscoverstheentirefieldofoptoelectronics,andhasbecomethecoretechnologyoftoday’soptoelectronics.Semiconductorlasersareusedinlaserranging,laserradar,lasercommunications,lasersimulationweapons,laserwarning,laserguidedtracking,ignitionanddetonation,andautomaticControlanddetectioninstrumentshavebeenwidelyused,formingabroadmarket.In1978,semiconductorlasersbegantobeusedinopticalfibercommunicationsystems.Semiconductorlaserscanbeusedaslightsourcesandindicatorsforopticalfibercommunicationandformphotoelectricsubsystemsthroughlarge-scaleintegratedcircuitplanartechnology.Becausesemiconductorlasershaveexcellentcharacteristicsofultra-small,highefficiencyandhigh-speedoperationTherefore,thedevelopmentofthistypeofdevicehasbeencloselyintegratedwithopticalcommunicationtechnologyfromthebeginning.Itisusedinopticalcommunication,opticalconversion,opticalinterconnection,parallellightwavesystem,opticalinformationprocessingandopticalstorage,opticalcouplingofopticalcomputerperipheralequipment,etc.Ithasimportantuses.Theadventofsemiconductorlasershasgreatlypromotedthedevelopmentofinformationoptoelectronicstechnology.Uptonow,itisthefastestgrowingandmostimportantimportantlightsourceforlaserfibercommunicationsinthefieldofopticalcommunications.SemiconductorlaserspluslowlossOpticalfiberhashadasignificantimpactonopticalfibercommunicationandaccelerateditsdevelopment.Therefore,itcanbesaidthatwithouttheemergenceofsemiconductorlasers,therewouldbenoopticalcommunicationtoday.GaAs/AlGaAsdoubleheterojunctionlasersareimportantforopticalfibercommunicationandatmosphericcommunication.Lightsource,nowadays,alllong-distance,large-capacityopticalinformationtransmissionsystemsallusedistributedfeedbacksemiconductorlasers(DFB-LD).Semiconductorlasersarealsowidelyusedinopticaldisktechnology.Opticaldisktechnologyisacollectionofcomputingtechnology,lasertechnologyandAcomprehensivetechnologyintegratingdigitalcommunicationtechnology.Itisalarge-capacity,high-density,fast,effective,andlow-costinformationstoragemethod.Itrequiresalightbeamgeneratedbyasemiconductorlasertowriteandreadinformation.

Excitationmethod

①Opticalpumplaser.Referstolasersexcitedbyanopticalpump,includingalmostallsolid-statelasersandliquidlasers,aswellasafewgaslasersandsemiconductorlasers.②Electricallyexcitedlaser.Mostgaslasersareexcitedbygasdischarge(DCdischarge,ACdischarge,pulsedischarge,electronbeaminjection),andmostcommonsemiconductorlasersareexcitedbyjunctioncurrentinjection,andsomesemiconductorlaserscanalsobeusedExcitationbyhigh-energyelectronbeaminjection.③Chemicallaser.Thisrefersspecificallytoalaserthatusestheenergyreleasedbyachemicalreactiontoexcitetheworkingsubstance.Thechemicalreactionthatisexpectedtobegeneratedcanbeinitiatedbylight,discharge,andchemicalrespectively.④Nuclearpumplaser.Referstoaspecialtypeoflaserthatusestheenergyreleasedbyasmallnuclearfissionreactiontoexciteworkingmaterials,suchasanuclear-pumpedhelium-argonlaser.

Operationmethod

Duetothedifferentworkingmaterials,excitationmethodsandapplicationpurposesofthelaser,theoperationmodeandworkingstatearealsodifferent,whichcanbedividedintothefollowingThemaintypes.①Continuouslaser,itsworkingcharacteristicistheexcitationoftheworkingsubstanceandthecorrespondinglaseroutput,whichcanbecontinuouslycarriedoutinacontinuousmanneroveralongperiodoftime.Thesolid-statelaserexcitedbythecontinuouslightsourceandthegaslaserworkinginthecontinuouselectricalexcitationmodeAndsemiconductorlasersfallintothiscategory.Astheoverheatingeffectofthedeviceisinevitablyproducedduringcontinuousoperation,itisnecessarytotakeappropriatecoolingmeasuresinmostcases.②Singlepulselaser.Forthistypeoflaser,theexcitationoftheworkingmaterialandthecorrespondinglaseremissionarebothasinglepulseprocessintermsoftime.Generalsolidlasers,liquidlasersandsomespecialgaslasers,Allofthemareoperatedinthisway.Atthistime,thethermaleffectofthedevicecanbeignored,sospecialcoolingmeasuresmaynotbetaken.③Repetitivepulselaser.Thecharacteristicofthistypeofdeviceisthatitsoutputisaseriesofrepetitivelaserpulses.Forthisreason,thedevicecanbeexcitedbyrepetitivepulses,orbeexcitedinacontinuousmannerbutmodulatethelaseroscillationprocessinacertainwaytoObtainingrepetitivepulselaseroutputusuallyrequireseffectivecoolingmeasuresforthedevice.④Q-switchedlaser,whichspecificallyreferstoapulsedlaserthatusesacertainswitchingtechnologytoobtainahigheroutputpower.Itsworkingprincipleistonotcauselaseroscillationafterthepopulationinversionstateoftheworkingsubstanceisformed(theswitchisclosed)State),afterthenumberofparticleshasaccumulatedtoasufficientlyhighlevel,theswitchissuddenlyandinstantaneouslyopened,sothataverystronglaseroscillationandhigh-powerpulsedlaseroutputcanbeformedinarelativelyshortperiodoftime(forexample,10to10seconds)(seeTechnology'"class=link>lasertuningtechnology).⑤Mode-lockedlaser,whichisaspecialtypeoflaserthatadoptsmode-lockingtechnology.Itsworkingcharacteristicisthatthereisacertainphaserelationshipbetweendifferentlongitudinalmodesintheresonantcavity,soitcanbeobtainedAseriesoflaserultrashortpulses(pulsewidth10~10seconds)areequallyspacedintime.Ifaspecialfastopticalswitchtechnologyisfurtherused,asingleultrashortlaserpulsecanbeselectedfromtheabovepulsesequence(Seelasermode-lockingtechnology).⑥Single-modeandfrequency-stabilizedlasers.Single-modelasersrefertolasersthatoperateinsingletransversemodeorsingle-longitudinalmodeafteradoptingcertainmode-limitingtechnology.Frequency-stabilizedlasersrefertotheuseofcertainautomaticControlmeasuresmakethelaseroutputwavelengthorfrequencystabilizedinaspeciallaserdevicewithinacertainaccuracyrange.Insomecases,itcanalsobemadeintoaspeciallaserdevicethatisbothsingle-modeoperationandhastheabilitytoautomaticallystabilizethefrequency(seeLaserFrequencyStabilizationTechnology).⑦Tunablelasers,undernormalcircumstances,theoutputwavelengthofthelaserisfixed,butaftertheuseofspecialtuningtechnology,theoutputlaserwavelengthofsomelaserscanbecontinuouslyandcontrollablygeneratedwithinacertainrangeChange,thistypeoflaseriscalledtunablelaser(seelasertuningtechnology).

Bandrange

Accordingtothedifferentoutputlaserwavelengthrange,varioustypesoflaserscanbedividedintothefollowingThereareseveraltypes.①Far-infraredlasers,whoseoutputwavelengthrangeisbetween25and1000microns,andthelaseroutputofsomemoleculargaslasersandfreeelectronlasersfallintothisarea.②Mid-infraredlasersrefertotheoutputlaserwavelengthinthemid-infraredLaserdevicesintheregion(2.5-25microns),representedbyCO2moleculargaslaser(10.6microns),COmoleculargaslaser(5-6microns).③Near-infraredlasermeansthattheoutputlaserwavelengthisinthenear-infraredregion(0.75~2.5micron)laserdevices,representedbyneodymium-dopedsolid-statelasers(1.06microns),CaAssemiconductordiodelasers(about0.8microns)andcertaingaslasers,etc.④Visiblelasersrefertotheoutputlaserwavelengthinthevisiblespectralregion(4000～7000Angstromsor0.4～0.7microns)ofaclassoflaserdevices.Representativesareruby​​lasers(6943angstroms),helium-neonlasers(6328angstroms),argonionlasers(4880angstroms,5145angstroms),kryptonionlasers(4762angstroms,5208angstroms,5682angstroms,6471angstroms)andsometunabledyelasers,etc.⑤Near-ultravioletlaser,itsoutputlaserwavelengthrangeInthenear-ultravioletspectralregion(2000～4000angstroms),therepresentativesarenitrogenmolecularlaser(3371angstroms)xenonfluoride(XeF)excimerlasers(3511angstroms,3531angstroms),kryptonfluoride(KrF)excimerlasers(2490)Angstroms)andsometunabledyelasers.⑥Vacuumultravioletlaser,whoseoutputlaserwavelengthrangeisinthevacuumultravioletspectralregion(50～2000angstroms).Representativesare(H)molecularlaser(1644～1098angstrom),xenon(Xe)excimerlaser(1730angstrom),etc.⑦X-raylaserreferstoalasersystemwhoseoutputwavelengthisintheX-rayspectrum(0.01-50angstroms).SoftX-rayshavebeensuccessfullydeveloped,buttheyarestillintheexploratorystage.

Historicalorigin

Theinventionofthelaserisamajorachievementofscienceandtechnologyinthe20thcentury.Itmakespeoplefinallyhavetheabilitytodrivethelight-emittingprocessofmoleculesandatomswithextremelysmallscales,extremelylargenumbers,andextremelychaoticmotions,soastoobtaintheabilitytogenerateandamplifycoherentinfrared,visibleandultraviolet(andevenX-raysandgammarays).Theriseoflaserscienceandtechnologyhasbroughtmankind'sunderstandingandutilizationoflighttoanewlevel.Thebirthhistoryoflaserscanberoughlydividedintoseveralstages,amongwhichtheconceptofstimulatedemissionproposedbyEinsteinin1916isitsimportanttheoreticalbasis.Thistheorystatesthatamaterialparticleinahigh-energystatewillbeconvertedtoalow-energystatebyaphotonwhoseenergyisequaltotheenergydifferencebetweenthetwoenergylevels,andasecondphotonwillbeproduced,whichisemittedatthesametimeasthefirstphoton.Thisisstimulatedemission.Thelightoutputbythisradiationisamplifiedandiscoherentlight,thatis,theemissiondirection,frequency,phase,andpolarizationofmultiplephotonsareexactlythesame.

Developmentstage

Sincethen,theestablishmentanddevelopmentofquantummechanicshasenabledpeopletohaveadeeperunderstandingofthemicrostructureandmotionlawsofmatter,theenergyleveldistribution,transitionandIssuessuchasphotonradiationhavealsobeenmorepowerfullyproved,whichalsoobjectivelyperfectsEinstein'sstimulatedemissiontheoryandfurtherlaysthetheoreticalfoundationfortheproductionoflasers.Afterthebirthofquantumelectronicsinthelate1940s,itwasquicklyappliedtostudytheinteractionbetweenelectromagneticradiationandvariousmicroscopicparticlesystems,andmanycorrespondingdevicesweredeveloped.Therapiddevelopmentofthesescientifictheoriesandtechnologieshavecreatedconditionsfortheinventionoflasers.

Iftherearemoreparticlesinahigh-energystatethaninalow-energystateinasystem,therewillbeastateofinversionofthenumberofparticles.Soaslongasthereisaphoton,itwillforceanatominahigh-energystatetobestimulatedtoemitthesamephoton,andthesetwophotonswilltriggerthestimulatedradiationofotheratoms,thusrealizingtheamplificationoflight;ifyouaddThefeedbackeffectoftheappropriateresonantcavitywillformopticaloscillation,therebyemittinglaserlight.Thisishowthelaserworks.In1951,AmericanphysicistsPurcellandPoundsucceededincausingapopulationinversioninanexperimentandobtainedstimulatedemissionof50kilohertzpersecond.Later,AmericanphysicistCharlesTownsandSovietphysicistsMasovandProkhorovsuccessivelyproposeddesignsthatusetheprincipleofstimulatedemissionofatomsandmoleculestogenerateandamplifymicrowaves.

However,mostoftheabove-mentionedtheoryandexperimentalresearchofmicrowavespectroscopybelongedto"purescience".Itwasstillveryuncertainwhetherthelasercouldbesuccessfullydevelopedornot.

Maturestage

Butthescientists'effortsfinallyyieldedresults.In1954,theaforementionedAmericanphysicistTownsfinallymadethefirstammoniamolecularbeammaser,successfullysettingaprecedentfortheuseofmolecularandatomicsystemsascoherentamplifiersoroscillatorsformicrowaveradiation.

ThemaserdevelopedbyTownsetal.onlygeneratesmicrowaveswithawavelengthof1.25cm,andthepowerisverysmall.Thecontinuousdevelopmentofproductionandtechnologyrequiresscientiststoexplorenewlight-emittingmechanismstoproducenewlightsourceswithexcellentperformance.In1958,Townsandhisbrother-in-lawArthurXiaoLuocombinedthemaserwiththetheoreticalknowledgeofopticsandspectroscopy,andputforwardkeyrecommendationsfortheuseofopenresonantcavities,andpreventedthecoherenceanddirectivityofthelaser.,Linewidthandnoise.Atthesametime,Basov,Prokhorovandothersalsoproposedaprincipleschemeforrealizingstimulatedemissionlightamplification.

Sincethen,manylaboratoriesintheworldhavebeeninvolvedinafiercedevelopmentcompetitiontoseewhocansuccessfullymanufactureandoperatetheworld'sfirstlaser.

In1960,theAmericanphysicistTheodorMaymanbarelywonthisworldwidedevelopmentcompetitioninhisresearchlaboratoryinMiami,Florida.Heusedahigh-strengthflashtubetostimulatethechromiumatomsintheruby​​crystal,therebyproducingafairlyconcentratedslenderredbeamoflight,whichwhenitisshotatacertainpoint,canmakethispointreachatemperaturehigherthanthesun.

The"Maymandesign"hasarousedshockandsuspicioninthescientificcommunity,becausescientistshavebeenwatchingandlookingforwardtothehelium-neonlaser.

AlthoughMaymanwasthefirstscientisttointroducelasersintothepracticalfield,thedisputeincourtaboutwhoinventedthetechnologyoncecausedgreatcontroversy.OneofthecompetitorsisGordonGould,theinventoroftheterm"laser"(abbreviationof"stimulatedemissionopticalfrequencyamplifier").HecameupwiththistermwhenhewasstudyingforaPhDatColumbiaUniversityin1957.Atthesametime,TownsandXiaoLuo,theinventorsofthemaser,alsodevelopedtheconceptoflasers.ThecourtfinallydecidedthatTownsbecamethewinnerbecauseofhiswrittenworkninemonthsearlierthanGould.However,Mayman'slaserinventionrightshavenotbeenshaken.

InDecember1960,theAmericanscientistJawanShuren,borninIran,finallysucceededinmanufacturingandoperatingtheworld'sfirstgaslaser-helium-neonlaser.In1962,threegroupsofscientistsinventedthesemiconductorlaseralmostsimultaneously.In1966,scientistsdevelopedanorganicdyelaserwhosewavelengthcouldbeadjustedcontinuouslywithinacertainrange.Inaddition,therearechemicallaserswithhighoutputenergyandhighpower,andtheydonotrelyonpowergrids.

Mainpurpose

Laserisoneoftheessentialcorecomponentsinmodernlaserprocessingsystem.Withthedevelopmentoflaserprocessingtechnology,lasersarealsoconstantlymovingforward,andmanynewlasershaveappeared.Earlylaserprocessinglasersweremainlyhigh-powerCO2gaslasersandlamp-pumpedsolid-stateYAGlasers.Fromtheperspectiveofthedevelopmenthistoryoflaserprocessingtechnology,thefirstlasertoappearwasthesealed-offCO2lasertubeinthemid-1970s.Sofar,thefifthgenerationofCO2laser-diffusioncoolingCO2laserhasappeared.ItcanbeseenfromthedevelopmentthattheearlyCO2laserstendedtoincreasethelaserpower,butwhenthelaserpowerreachedacertainrequirement,thebeamqualityofthelaserwaspaidattentionto,andthedevelopmentofthelasershiftedtotheimprovementofthebeamquality.Theemergingdiffusion-cooledslabCO2laser,whichisclosetothediffractionlimit,hasgoodbeamquality.Ithasbeenlaunchedandhasbeenwidelyused,especiallyinthefieldoflasercutting,andisfavoredbymanycompanies.

Atthebeginningofthe21stcentury,anothernewtypeoflaser,asemiconductorlaser,appeared.Comparedwithtraditionalhigh-powerCO2,YAGsolid-statelasers,semiconductorlasershaveobvioustechnicaladvantages,suchassmallsize,lightweight,highefficiency,lowenergyconsumption,longlife,andhighabsorptionofsemiconductorlasersbymetals.Withthecontinuousdevelopmentoflasertechnology,othersolid-statelasersbasedonsemiconductorlasers,suchasfiberlasers,semiconductor-pumpedsolid-statelasers,andsheetlasers,havealsodevelopedrapidly.Amongthem,fiberlasersaredevelopingrapidly,especiallyrare-earth-dopedfiberlasers,whichshouldhavebeenwidelyusedinthefieldsoffibercommunications,fibersensing,andlasermaterialprocessing.

Duetotheoutstandingcharacteristicsoflasers,theywerequicklyusedinindustry,agriculture,precisionmeasurementanddetection,communicationandinformationprocessing,medicaltreatment,militaryandotheraspects,andcausedrevolutioninmanyfields.Breakthrough.Inadditiontothemilitaryuseoflasersforcommunications,nightvision,earlywarning,ranging,etc.,avarietyoflaserweaponsandlaserguidedweaponshavealsobeenputintopracticaluse.

1.Thelaserisusedasaheatsource.Thelaserbeamissmallandcarriesahugeamountofpower.Ifitisfocusedbyalens,itcanconcentratetheenergyonatinyareaandgeneratehugeheat.Forexample,peoplecanusetheconcentratedandextremelyhighenergyoflasertoprocessvariousmaterials,andcandrill200holesinaneedle;laserasakindofeffectonbiologicalorganismssuchasstimulation,mutation,burning,vaporization,etc.Themethodhasachievedgoodresultsinthepracticalapplicationofmedicineandagriculture.

2.Laserranging.Asthelightsourcefordistancemeasurement,thelasercanmeasurealongdistanceduetoitsgooddirectivityandhighpower,anditsaccuracyisveryhigh.

3.Lasercommunication.Inthefieldofcommunication,alightguidecablethatusesalaserbeamtotransmitsignalscancarrytheamountofinformationequivalentto20,000telephonecopperwires.

4.Applicationofcontrollednucleargatheringair.Whenthelaserisshotintothemixtureofdeuteriumandtritium,thelasergivesthemhugeenergy,generateshighpressureandhightemperature,promotesthepolymerizationoftwonucleiintoheliumandneutrons,andemitshugeradiantenergyatthesametime.Becausethelaserenergycanbecontrolled,thisprocessiscalledcontrollednuclearfusion.

Inthefuture,withthefurtherresearchanddevelopmentoflasertechnologybymankind,theperformanceoflaserwillbefurtherimproved,andthecostwillbefurtherreduced,butitsapplicationrangewillcontinuetoexpand,anditwillplaymoreandmoreThegreatertheeffect.

Laserpointerisasmalllow-powerlaserthatuseslaserasapointer.Itisageneralcivilianproduct,andisalsocalledlaserpointer,starpointer,etc.Itisaproductwithawiderangeofuses:teachingandscientificresearchunitsareusedforteaching,academicreports,conferencesandotheroccasionswithvideoequipmentasinstructions;militaryunitsareusedtocooperatewithlarge-screencommandsysteminstructions;touristunitsareusedfortourguides;constructionanddecorationThesupervisionunitisusedforinstructionsduringconstructionanddecorationacceptance.Onsomeoccasions,itcanalsobefixedasadirectionaltool;itcanalsobeusedasagift.

Summary

Therearealsomanytypesofcarbondioxidelasersthatemitpulses,whichareextremelyversatileinscientificresearchandindustry.Ifyoucomparetheenergyemittedbyeachpulse,thepulsedcarbondioxidelaseristhestrongestamongpulsedlasers.Here,wearegoingbacktotheproblemthatthelaserpioneerTownsoncestudied,andtalkaboutthegenerationofmillimeterwaves.Withthedevelopmentoflasertechnology,manyscientistshavelaunchedanattackonthisproblem:useelectricdischargeoruseapowerfulcarbondioxidelaserasanexcitationsourcetoexcitegasmoleculessuchasfluoromethaneandammonia,andstepbysteptoextendthewavelengthoftheemittedlaser.Extension.Atfirstitreachedtensofmicrometers,andlaterreachedseveralhundredsofmicrometers,thatis,sub-millimeterwaves.Fromthemid-1960stothemid-1970s,withthedevelopmentofmicrowavetechnology,scientistsgeneratedmillimeterwavesbasedontheprinciplesandmethodsoflasers.Inthisway,thegapbetweenlightwavesandmicrowavesisfilledbynewinfraredlasersthatareconstantlybeingdiscovered.

Fromresearch,scientistshavefoundthatmillimeterwavesareofgreatpracticalvalue:theabsorptionrateoftheatmosphereisverysmall,andtheinfluenceofhinderingitspropagationissmall,anditcanbeusedasanewatmosphericcommunicationtool.

Anotherspecialandnovellasercanbecalled"chameleon"vividly.Itisnotadragon,butitcanchangecolor;aslongasyouturnaknobonthelaser,youcangetlasersinvariouscolorsofred,orange,yellow,green,blue,indigo,andpurple.

Isthereanyrelationshipbetweendyesandlasers?Notbadatall.Theworkingmaterialsofthislaserareindeeddyes,suchascarbocyanine,rhodamine,coumarinandsoon.Scientistshavenotyetfiguredoutthemolecularenergylevelsandatomicstructureofthesedyes.Theyonlyknowthattheyaredifferentfromthegasatomandionstructureofthegasworkingsubstance;thelasergeneratedbythegashasaclearwavelength,whilethelasergeneratedbythedyehasashorterwavelengthrange.Wide,ortherearemanycolors.Theopticalresonantcavityofthedyelasercontainsanopticalelementcalledagrating.Throughit,youcanchoosethecolorofthelaseraccordingtoyourneeds,justlikelisteningtoradiostationsofdifferentfrequenciesfromaradio.

Futureoutlook

Theexcitationsourceofthedyelaserisanopticalpump,whichcanbeapulsedxenonlamporalaserfromanitrogenmolecularlaser.Oneofthecharacteristicsofdyelasersistousealaserofonecolorastheopticalpump,andasaresultcanproducelasersofothercolors.

Thiskindoflaser,whichcanchangethewavelengthofthelaserlightatanytimeasneeded,ismainlyusedforspectroscopyresearch;manysubstanceswillselectivelyabsorblightofcertainwavelengthsandcauseresonance.Scientistsusethesephenomenatoanalyzematterandunderstandthestructureofmaterials;theyalsousetheselaserstogeneratenewlasersandstudysomestrangeopticalandspectroscopicphenomena.

Pronetoaccidents

Whenusingalasercuttingmachine,thelasershotofthelasermaycausethefollowingaccidents:

(1)Thelasershotiscausedbyflammablematerials.Fire.Everyoneknowsthatthepowerofthelasergeneratorisveryhigh,especiallywhenitcomestohigh-powerlasercuttingmachines,thetemperatureofthelaserlightemittedisveryhigh.Itisverylikelytocauseafirewhenthelaserhitsflammableobjects.

(2)Harmfulgasmaybegeneratedwhenthemachineisrunning.Forexample,whenoxygenisusedforcutting,achemicalreactionoccurswiththecuttingmaterial,resultinginimpuritiessuchasunknownchemicalsubstancesorfineparticles.Afterbeingabsorbedbythehumanbody,itmaycauseallergicreactionsorcauserespiratorydiscomfortsuchasthelungs.Protectivemeasuresshouldbetakenduringoperations.

(3)Directlaserirradiationwillbeharmfultothehumanbody.Thedamageoflasertohumanbodymainlyincludesdamagetoeyesandskin.Amongthelaserinjuries,thebody'sdamagetotheeyesisthemostserious.Andthedamagetotheeyesispermanent.Therefore,youmustpayattentiontoprotectingyoureyeswhenworking.

Therefore,inthecuttingenvironment,flammableobjectsshouldbestrictlyprohibitedfromapproachingthemachineandshouldbeventilated.Theworkplaceshouldalsobeequippedwithafireextinguisher.Workersmusttakeself-protectionmeasureswhenperformingoperations.

Prospects

Fiberlaserscanachievelaseroutputinthe800nm-2100nmband,andthemaximumpowerhasreachedtheorderof10,000watts.Theapplicationhasalsoexpandedfromopticalcommunicationstolaserprocessingandlasermarking.,Imagedisplay,bioengineering,medicalandhealthandotherfields.Thefuturedevelopmenttrendoffiberlaserswillbereflectedinthefollowingaspects:

(1)Improvementoffiberlaserperformance:howtoimproveoutputpowerandconversionefficiency,optimizebeamquality,shortengainfiberlength,andimprovesystemStabilityandmakingitmorecompactandcompactwillbethefocusoffutureresearchinthefieldoffiberlasers.

(2)Developmentofanewtypeoffiberlaser:Inthetimedomain,ultrashortpulsemode-lockedfiberlaserswithasmallerdutycyclehavealwaysbeenahotspotinthelaserfield.High-powerfemtosecondpulsesFiberlasershavealwaysbeenalong-termgoalpursuedbypeople.Researchbreakthroughsinthisfieldcannotonlyprovideideallightsourcesforopticalcommunicationtimedivisionmultiplexing(OTDM),butalsoeffectivelydrivethedevelopmentoflaserprocessing,lasermarkingandlaserencryptionandotherrelatedindustries.Inthefrequencydomain,broadbandoutputandtunablefiberlaserswillbecomearesearchhotspot.AnonlinearfiberlaserusingZEBLANmaterials(Zr,Ba,La,Al,Nd)asthelasermediumhasattractedpeople’sattention.Ithasafairlywidebandwidthandlowloss,andcanachievewavelengthup-conversioninseveralbands.Itispraisedbyexpertsasthenextgenerationofcommunicationmaterials.Ifmassproductioncanbeachieved,itwillgenerateamarketofbillionsofdollarsinthefieldoflaserprintingandlarge-screendisplays..Itisforeseeablethatwiththeimprovementofrelatedtechnologies,fiberlaserswilldevelopintoabroaderfield,andmaybecomeanewgenerationoflightsourcestoreplacesolid-statelasersandsemiconductorlasers,forminganewindustry.

Classification

Tunablelaser

Tunablelaserreferstoalaserthatcancontinuouslychangethelaseroutputwavelengthwithinacertainrange(seelaser).Thiskindoflaserhasawiderangeofuses,suchasspectroscopy,photochemistry,medicine,biology,integratedoptics,pollutionmonitoring,semiconductormaterialprocessing,informationprocessing,andcommunications.

Single-modelaser

Theoutputisasingletransversemode(usuallyfundamentalmode),multi-longitudinalmodelaser.

ChemicalOxygenIodineLaser

ChemicalOxygenIodineLaserisanairbornelaser.TheairbornelasersystemisbasedonamodifiedBoeing747-400Faircraftasthelaunchplatform(code-namedYAL-1A),withachemicaloxygen-iodinelaserthatproduceshigh-energylasersasthecore,equippedwithtrackingandaimingsystemsandbeamcontrolandlaunchsystems,usinglasersastheAdirectedenergyweaponthatdirectlydamagesthetargetorrendersitineffective.

Carbondioxidelaser

CarbondioxidelaserisagaslaserwithCO2gasasitsworkingsubstance.Thedischargetubeisusuallymadeofglassorquartzmaterial,filledwithCO2gasandotherauxiliarygases(mainlyheliumandnitrogen,andusuallyasmallamountofhydrogenorxenon);theelectrodeisgenerallyahollowcylindermadeofnickel;resonantcavityOneendisagold-platedtotalreflectionmirror,andtheotherendisapartialreflectionmirrorpolishedwithgermaniumorgalliumarsenide.Whenahighvoltage(usuallyDCorlow-frequencyAC)isappliedtotheelectrode,aglowdischargeisgeneratedinthedischargetube,andthereisalaseroutputatoneendofthegermaniummirror,anditswavelengthisinthemid-infraredbandnear10.6microns;generallyabettertube.Adischargeareaof​​aboutonemeterlongcanobtainacontinuousoutputpowerof40to60watts.CO2laserisarelativelyimportantgaslaser

Liquidlaser

Liquidlaserisalsocalleddyelaser,becausetheactivematerialofthistypeoflaserissomeorganicdyesdissolvedinethanolandmethanol.Orasolutionformedinaliquidsuchaswater.Inordertoexcitethemtoemitlasers,high-speedflashlampsaregenerallyusedaslasersources,orotherlasersemitshortlightpulses.Thelaserlightemittedbytheliquidlaserisofgreatsignificanceforspectralanalysis,laserchemistry,andotherscientificresearch.

Digitallaser

Thedigitallaserreplacesoneofthemirrorswitha"spatiallightmodulator".The"spatiallightmodulator"islikeareflectiveminiatureliquidcrystaldisplay,"youonlyneedtoinputaspecificimagetothedisplaythroughthecomputertogettherequiredlasermode.Itsbiggestfeatureisthatthereisnoneedtodesignanewlaserforeachlaser.Justchangethepictureonthecomputertogetthebeamshapeyouwant.

Digitallaserscancreatealmostanylaserpattern.Inthepast,eachbeamoflightrequiredaseparatelaser.Forthisreason,manypeopleIttakesayearortwotodoit.

Thisinventionisamilestoneinlasertechnology.Inthemedicalfield,itcanbeusedforbloodlesssurgery,eyecareanddentistry.Intheindustrialfield,itcanhelpCutting,welding.Inthefieldofcommunications,itwillgreatlypromotethedevelopmentofopticalfibercommunications.