超快光学放大演示文稿

超快光学放大演示文稿第一页，共四十九页。Pulseenergyvs.RepetitionrateReprate(pps)Pulseenergy(J)10910610310010-310-910-610010-3OscillatorCavity-dumpedoscillatorRegARegenRegen+multipassRegen+multi-multi-pass1Waveragepower第二页，共四十九页。AtWhatarethegoalsinultrashortpulseamplification?Ipeak=EIncreasetheenergy(E),Decreasetheduration(t),Decreasetheareaofthefocus(A).MaximumintensityontargetNeededtostarttheexperimentNeededtogetusefulresultsPave=ErSignalisproportionaltothenumberofphotonsonthedetectorperintegrationtime.MaximumaveragepoweratthedetectorPulseenergyRepratePulseenergyBeamareaPulselength第三页，共四十九页。IssuesinUltrafastAmplificationandTheirSolutionsPulselengthdiscrepancies:Multi-passamplifiersandregenerativeamplifiers(“Regens”).Damage:Chirped-PulseAmplification(CPA)Gainsaturation:Frantz-NodvickEquationGainnarrowing:BirefringentfiltersThermaleffects:coldandwavefrontcorrectionSatellitepulses,Contrast,andAmplifiedSpontaneousEmission:Pockels’cellsSystemscostlotsofmoney:Earnmoremoney…Pockelscellpolarizergainpumpinput/output第四页，共四十九页。CavityDumpingBeforeweconsideramplification,recallthattheintracavitypulseenergyis~50timestheoutputpulseenergy.Sowehavemorepulseenergy.Howcanwegetatit?Whatifweinsteadusedtwohighreflectors,letthepulseenergybuildup,andthenswitchoutthepulse?ThisistheoppositeofQ-switching:itinvolvesswitchingfromminimumtomaximumloss,andit’scalled“CavityDumping.”E=ToutputEintracavityTransmissionofoutputcoupler:~2%R=100%R=98%EintracavityE第五页，共四十九页。Cavitydumping:thePockelscellAPockelscellisadevicethatcanswitchapulse(inand)outofaresonator.It’susedinQ-switchesandcavitydumpers.Avoltage(afewkV)canturnacrystalintoahalf-orquarter-waveplate.VIfV=0,thepulsepolarizationdoesn’tchange.IfV=Vp,thepulsepolarizationswitchestoitsorthogonalstate.AbruptlyswitchingaPockelscellallowsustoextractapulsefromacavity.Thisallowsustoachieve~100timesthepulseenergyat1/100therepetitionrate(i.e.,100nJat1MHz).Pockelscell(voltagemaybetransverseorlongitudinal)Polarizer第六页，共四十九页。AmplificationofLaserPulses,inGeneralVerysimply,apowerfullaserpulseatonecolorpumpsanamplifiermedium,creatinganinversion,whichamplifiesanotherpulse.Nanosecond-pulselaseramplifierspumpedbyothernslasersarecommonplace.LaseroscillatorAmplifiermediumPumpEnergylevelsJpump(lpump/lL)lLlpump第七页，共四十九页。Single-passAmplificationMathAssumeasaturablegainmediumandJisthefluence(energy/area).Assumeallthepumpenergyisstoredintheamplifier,butsaturationeffectswilloccur.Atlowintensity,thegainislinear:Athighintensity,thegain“saturates”andhenceisconstant:Intermediatecaseinterpolatesbetweenthetwo:AmplifiermediumpumpJinJpumpJoutJsatlLlpumpJstoJsto=storedpumpfluence=Jpump(lpump/lL)Jsat=saturationfluence(materialdependent)第八页，共四十九页。Single-passAmplificationMathwherethesmallsignalgainperpassisgivenby:ThisdifferentialequationcanbeintegratedtoyieldtheFrantz-Nodvickequationfortheoutputofasaturatedamplifier:第九页，共四十九页。Frantz-NodvickequationG0exp(g0L)exp(JstoJsat)Higherpumping(Jsto)meanshigherefficiencyandhighersaturationandsolowergain.Soyoucanhavehighgainorhighextractionefficiency.Butnotboth.11,21,41,61,822,22,42,600,20,40,60,81012345GainExtractionefficiency(Jout/Jsto)Jsto/JsatJout/Jin第十页，共四十九页。Anotherproblemwithamplifyingultrashortlaserpulses…Anotherissueisthattheultrashortpulseissomuchshorterthanthe(nsorms)pumppulsethatsuppliestheenergyforamplification.Soshouldtheultrashortpulsearriveearlyorlate?Early:Late:Pumpenergyarrivestoolateandiswasted.timepumppumptimeEnergydecaysandiswasted.Inbothcases,pumppulseenergyiswasted,andamplificationispoor.第十一页，共四十九页。Soweneedmanypasses.Allultrashort-pulseamplifiersaremulti-pass.Thisapproachachievesmuchgreaterefficiency.timepumpTheultrashortpulsereturnsmanytimestoeventuallyextractmostoftheenergy.第十二页，共四十九页。TwomainamplificationmethodsMulti-passamplifierpumpinputoutputgainPockelscellpolarizergainpumpinput/outputRegenerativeamplifier第十三页，共四十九页。Anothermulti-passamplifierAPockelscell(PC)andapairofpolarizersareusedtoinjectasinglepulseintotheamplifier.第十四页，共四十九页。RegenerativeamplifiergeometriesThisisusedfor10-20-Hzrepetitionrates.IthasalargerspotsizeintheTi:sapphirerod.PockelscellFaradayrotatorthin-filmpolarizerPockelscellTheTi:Sapphirerodis~20-mmlonganddopedfor90%absorption.ThisdesignisoftenusedforkHz-repetition-rateamplifiers.第十五页，共四十九页。Pulseintensitiesinsideanamplifiercanbecomesohighthatdamage(oratleastsmall-scaleself-focusing)occurs.Solution:Expandthebeamanduselargeamplifiermedia.Okay,wedidthat.Butthat’sstillnotenough.Solution:Expandthepulseintime,too.Okay,sowhatnext?第十六页，共四十九页。Chirped-PulseAmplificationChirped-pulseamplificationin-volvesstretchingthepulsebeforeamplifyingit,andthencompressingitlater.Wecanstretchthepulsebyafactorof10,000,amplifyit,andthenrecompressit!G.Mourouandcoworkers1983CPAisTHEbigdevelopment.PulsecompressorttSolidstateamplifiertDispersivedelaylinetShortpulseoscillator第十七页，共四十九页。Stretchingandcompressingultrashortpulsesdf2ffdgratinggratingOkay,thislooksjustlikea“zero-dispersionstretcher”usedinpulseshaping.Butwhend≠f,it’sadispersivestretcherandcanstretchfspulsesbyafactorof10,000!Withtheoppositesignofd-f,wecancompressthepulse.Pulsestretcher第十八页，共四十九页。ApulsestretcherThisdevicestretchesan18-fspulseto600ps—afactorof30,000!Araytraceofthevariouswavelengthsinthestretcher: Pulsestretchercharacteristics:Inputpulsewidth:18fsOutputpulseduration:600psBandwidthpassed:>105nmPulseenergyout:~0.5nJ第十九页，共四十九页。AlexandriteTi:sapphireExcimers0,00010,0010,010,11101001101001000104105106Nd:GlassDyesDirectAmplificationFluence(J/cm2)PulseDuration(fs)CPAvs.DirectAmplificationCPAachievesthefluenceoflongpulsesbutatashorterpulselength!第二十页，共四十九页。RegenerativeChirped-PulseAmplificationat~100kHzreprateswithacwpumpCoherentRegAamplifierAfsoscillatorrequiresonly~5Wofgreenlaserpower.AnArgonlaserprovidesupto50W.Usetheresttopumpanamplifier.Today,weuseanintracavity-doubledNd:YLFpumplaser(~10W).Microjoulesat250kHzrepetitionrates!第二十一页，共四十九页。Regenerativechirped-pulseamplificationwithakHzpulsedpump Wavelength:800nm(Repetitionratesof1to50kHz)HighEnergy:<130fs,>2mJat1kHzPicosecond:~80ps,>0.7mJat1kHzShortPulse:<50fs,>0.7mJat1kHzSpectraPhysicsregen:the“Spitfire”第二十二页，共四十九页。PumplaserforultrafastamplifiersCoherent“Corona”highpower,Q-switchedgreenlaserinacompactandmorereliablediode-pumpedpackage15mJ(ns)ata10kHzreprate(150Wavepower!)第二十三页，共四十九页。1kHz10kHz100kHz20mJ1.8mJ0.2mJ20W18W20W3mm1mm250µmExtractedenergyBeamdiameterPumppower100WAveragePowerReprateAveragepowerforhigh-powerTi:SapphireregensTheseaveragepowersarehigh.Andthispumppowerisalso.Ifyouwantsub-100fspulses,however,theenergieswillbeless.第二十四页，共四十九页。CPAisthebasisofthousandsofsystems.It’savailablecommerciallyinnumerousforms.Itworks!Buttherearesomeissues,especiallyifyoutrytopushforreallyhighenergies:Amplifiedspontaneousemission(ASE)Gainsaturation:gainvs.extractionefficiencyGainnarrowingThermalaberrationsContrastratioDamagethresholdvsextractionefficiency第二十五页，共四十九页。AmplifiedSpontaneousEmission(ASE)Fluorescencefromthegainmediumisamplifiedbefore(andafter)theultrashortpulsearrives.Thisyieldsa10-30nsbackgroundwithlowpeakpowerbutlargeenergy.Dependsonthenoisepresentintheamplifieratt=0ASEsharesthegainandtheexcitedpopulationwiththepulse.Amplificationreducesthecontrastbyafactorofupto10.第二十六页，共四十九页。GainNarrowing(andASE)Oneachpassthroughanamplifier,thepulsespectrumgetsmultipliedbythegainspectrum,whichnarrowstheoutputspectrum—andlengthensthepulse!Asaresult,thepulselengthens,anditcanbedifficulttodistinguishtheultrashortpulsefromthelongerAmplifiedSpontaneousEmission(ASE)第二十七页，共四十九页。GainnarrowingexampleTi:sapphiregaincrosssection10-fssech2pulsein00.20.40.60.8100.511.522.536507007508008509009501000NormalizedspectralintensityCrosssection(*10^-19cm^2)Wavelength(nm)65-nmFWHM32-nmFWHMFactorof2lossinbandwidthfor107gainMostTerawattsystemshave>1010smallsignalgainlongerpulseout第二十八页，共四十九页。BeatinggainnarrowingBirefringentplatePolarizerPolarizerEEEwithfilterwithoutfilterSpectrumWavelength(nm)Gain&modulation650850900Wavelength(nanometers)70075080011.522.595020%GainmodulationBeforeAfterIntroducesomelossatthegainpeaktooffsetthehighgainthere.GainandlossSpectrum:beforeandafter第二十九页，共四十九页。Gain-NarrowingConclusionGainnarrowingcanbebeaten.Wecanuseuptohalfofthegainbandwidthfora4-levelsystem.Sub-20fsinTi:sapphireSub-200fsinNd:glassSub-100fsinYb:XX第三十页，共四十九页。00.20.40.60.81750800850Intensity(arb.units)Wavelength(nm)Verybroadspectracanbecreatedthisway.A100-nmbandwidthat800nmcansupporta10-fspulse.第三十一页，共四十九页。Heatdepositioncauseslensingandsmall-scaleself-focusing.Thesethermalaberrationsincreasethebeamsizeandreducetheavailableintensity.Ipeak=EATWewantasmallfocusedspotsize,butthermalaberrationsincreasethebeamsize,nottomentionscrewingitup,too.Nowtheaveragepowermatters.Therepetitionrateiscrucial,andwe’dlikeittobehigh,buthighaveragepowermeansmorethermalaberrations…ThermalEffectsinAmplifiers第三十二页，共四十九页。Lowtemperatureminimizeslensing.CalculationsforkHzsystemsCryogeniccoolingresultsinalmostnofocalpowerInsapphire,conductivityincreasesanddn/dTdecreasesasTdecreases.Murnane,Kapteyn,andcoworkers第三十三页，共四十九页。StaticWave-frontCorrection2.5timesimprovementinpeakintensityhasbeenachievedCUOS第三十四页，共四十九页。DynamicCorrectionofSpatialDistortion50mmdiameter37actuatorsCUOS第三十五页，共四十九页。ContrastratioWhydoesittakeover2yearsbetweenthefirstannouncementofanewlasersourceandthefirstsuccessfulexperimentusingit?Becausethepulsehasleadingandfollowingsatellitepulsesthatwreakhavocinanyexperiment.Ifapulseof1018W/cm2peakpowerhasa“little”satellitepulseonemillionthasstrong,that’sstill1TW/cm2!Thiscandosomeseriousdamage!Ionizationoccursat1011W/cm2soat1021W/cm2weneeda1010contrastratio!第三十六页，共四十九页。MajorsourcesofpoorcontrastNanosecondscale:pre-pulsesfromoscillatorpre-pulsesfromamplifierASEfromamplifierPicosecondscale:reflectionsintheamplifierspectralphaseoramplitudedistortions第三十七页，共四十九页。0-1-2-3-4-5-6-7-8-9-10FrontBacktimeSpectralphaseaberrationsPre-pulsesASE0ps10nsnsFWHMAmplifiedpulsesoftenhavepoorcontrast.Log(Energy)Pre-pulsesdothemostdamage,messingupamediumbeforehand.第三十八页，共四十九页。Typical3rd-orderautocorrelationAmplifiedpulseshavepre-andpost-pulses.第三十九页，共四十九页。APockelscell“PulsePicker”APockelscellcanpickapulsefromatrainandsuppresssatellites.Todoso,wemustswitchthevoltagefrom0tokVandbackto0,typicallyinafewns.VTimeVoltagefewnsSwitchinghighvoltagetwiceinafewnsisquitedifficult,requiringavalanchetransistors,microwavetriodes,orotherhigh-speedelectronics.第四十页，共四十九页。amplifieroscillatorstretchercompressorPockelscells10-2-10-310nsPockelscellssuppresspre-andpost-pulses.Unfortunately,Pockelscellsaren’tperfect.Theyleak~1%.第四十一页，共四十九页。ContrastimprovementrecipesAPockelscellimprovesthecontrastbyafew100to1000.Weneedatleast3Pockelscellsworkinginthebestconditions:onaxis(donottiltPockels’cells)broadbandhigh-contrastpolarizers(notdielectric)fastrisetime(<<2ns10-90%)collimatedbeamsTemperaturedriftisalsoaprobleminPockelscells.Also:Goodpumpsynchronizationgivesafactor3-10第四十二页，共四十九页。Multiple-stagemulti-passamplifiers1kHzMulti-passsystemattheUniversityofColorado(MurnaneandKapteyn)0.2TW4mJ,20fspulselength第四十三页，共四十九页。Closedloopcryogeniccooling100ºK5x1J,20HzNd:YAGlasers10fsoscillatorstretcher100HzRegenerativeamplifier200mJ,30fs,100HzHighenergy,highcontrast100-HzsystematCELIA第四十四页，共四十九页。PumpbeamUltrashortpulse--nearfieldUltrashortpulse--farfieldAmplified-pulsebeamshapes第四十五页，共四十九页。A1-JouleApparatus第四十六页，共四十九页。Multi-JouleSystemsNd:GlassEnergy>20JoulesPulsewidth<500fsPower>40TWRepetitionrates~everyhourTerawattLaserSystemTi:sapphireEnergy>1JoulePulsewidth<35fsPower>10TWRepetitionratesto1kHzYoucanbuytheselasers!第四十七页，共四十九页。LawrenceLivermoreNationalLabsHigh-PowerAmplifiersLaserSpecificationsUSP1996USP(InDevelopment)Janus1996TotalEnergy1Joule10Joule6-10JoulePulseLength100fs30-100fs600fsPeakIntensity5.e19W/cm25-10.e20W/cm25.e18W/cm2Wavelength800nm,400nm800nm,400nm1053nm,526nmPulseContrast<10-7in400nm<1.e-7in400nm<10-9in526nmRepRate1shotin3minutes1shotin20minutes1shotin3minutes第四十八页，共四十九页。EvenHigherIntensities!NationalIgnitionFacility(underconstruction)192shapedpulses10.4kJperbeaminUV(done)21kJperbeaminIR(done)>1.8MJtotalenergy(planned)Pulses0.2to25nsinlength第四十九页，共四十九页。