精编制作第八讲 超短脉冲强度测量PPT课件

1、Thegoal measuringtheintensityandphasevs time orfrequency Theways TheSpectrometerandMichelsonInterferometerScanningAutocorrelationSingle shotautocorrelationTheAutocorrelationandSpectrumThird orderAutocorrelationInterferometricAutocorrelation MeasuringUltrashortLaserPulsesI Autocorrelation Inordertomeasureaneventintime youneedashorterone Tostudythisevent youneedastrobelightpulsethat sshorter Butthen tomeasurethestrobelightpulse youneedadetectorwhoseresponsetimeisevenshorter Andsoon So now howdoyou

2、measuretheshortestevent PhotographtakenbyHaroldEdgerton MIT TheDilemma Ultrashortlaserpulsesaretheshortesttechnologicaleventsevercreatedbyhumans It sroutinetogeneratepulsesshorterthan10 13secondsinduration andresearchershavegeneratedpulsesonlyafewfs 10 15s long Suchpulseshavemanyapplicationsinphysics chemistry biology andengineering Youcanmeasureanyevent aslongasyou vegotapulsethat sshorter Sohowdoyoumeasurethepulseitself Youmustusethepulsetomeasureitself Butthatisn tgoodenough It sonlyasshortas

3、thepulse It snotshorter Techniquesbasedonusingthepulsetomeasureitselfhavenotsufficed Todeterminethetemporalresolutionofanexperimentusingit Todeterminewhetheritcanbemadeevenshorter Tobetterunderstandthelasersthatemitthemandtoverifymodelsofultrashortpulsegeneration Tobetterstudymedia thebetterweknowthelightinandlightout thebetterweknowthemediumwestudywiththem Tousepulsesofspecificintensityandphasevs timetocontrolchemicalreactions Coherentcontrol Tounderstandpulse shapingeffortsfortelecommunication

4、s etc Becauseit sthere Whymeasureanultrashortlaserpulse Asamoleculedissociates itsemissionchangescolor i e thephasechanges revealingmuchaboutthemoleculardynamics notavail ablefromthemerespectrum oreventheintensityvs time Linear Linearornonlinearmedium Measuringtheintensityandphaseofthepulsesintoandoutofamediumtellsusasmuchaspossibleaboutthelinearandnonlineareffectsinthemedium StudyingMediabyMeasuringtheIntensityandPhaseofLightPulses Withalinearmedium welearnthemedium sabsorptioncoefficientandref

5、ractiveindexvs Withanonlinear opticalmedium wecanlearnaboutself phasemodulation forexample forwhichthetheoryismuchmorecomplex Indeed theoreticalmodelscanbetested Time fs Intensity Phase Nonlinear Eaton etal JQE35 451 1999 Alaserpulsehasthetime domainelectricfield E I t 1 2 exp i w 0 t i t Intensity Phase t Re Equivalently vs frequency exp i j w w 0 Spectral Phase neglectingthenegative frequencycomponent E w Re S w w0 1 2 Wemustmeasureanultrashortlaserpulse sintensityandphasevs timeorfrequency Sp

6、ectrum Knowledgeoftheintensityandphaseorthespectrumandspectralphaseissufficienttodeterminethepulse t d dt Theinstantaneousfrequency Example Linearchirp We dliketobeabletomeasure notonlylinearlychirpedpulses butalsopulseswitharbitrarilycomplexphasesandfrequenciesvs time Thephasedeterminesthepulse sfrequency i e color vs time Thespectrometermeasuresthespectrum ofcourse Wavelengthvariesacrossthecamera andthespectrumcanbemeasuredforasinglepulse PulseMeasurementintheFrequencyDomain TheSpectrometer Co

7、llimatingMirror Czerny Turner arrangement EntranceSlit CameraorLinearDetectorArray FocusingMirror Grating Imagingspectrometers allowmanyspectratobemeasuredsimultaneously Broad bandpulse PulseMeasurementintheTimeDomain Detectors Examples Photo diodes Photo multipliers Detectorsaredevicesthatemitelectronsinresponsetophotons Detectorshaveveryslowriseandfalltimes 1nanosecond Asfaraswe reconcerned detectorshaveinfinitelyslowresponses Theymeasurethetimeintegralofthepulseintensityfrom to Thedetectorout

8、putvoltageisproportionaltothepulseenergy Bythemselves detectorstelluslittleaboutapulse Anothersymbolforadetector PulseMeasurementintheTimeDomain Varyingthepulsedelay Sincedetectorsareessentiallyinfinitelyslow howdowemaketime domainmeasurementsonorusingultrashortlaserpulses We lldelayapulseintime Andhowwillwedothat Bysimplymovingamirror Sincelighttravels300 mperps 300 mofmirrordisplacementyieldsadelayof2ps Thisisveryconvenient MovingamirrorbackwardbyadistanceLyieldsadelayof Donotforgetthefactorof

9、2 Lightmusttraveltheextradistancetothemirror andback Translationstage Inputpulse E t E t t Mirror Outputpulse Wecanalsovarythedelayusingamirrorpairorcornercube Mirrorpairsinvolvetworeflectionsanddisplacethereturnbeaminspace Butout of planetiltyieldsanonparallelreturnbeam Cornercubesinvolvethreereflectionsandalsodisplacethereturnbeaminspace Evenbetter theyalwaysyieldaparallelreturnbeam Hollowcornercubes avoidpropagationthroughglass EdmundScientific Measuringtheinterferogramisequivalenttomeasuring

10、thespectrum PulseMeasurementintheTimeDomain TheMichelsonInterferometer Pulseenergy boring Fieldautocorrelation maybeinteresting but TheFTofthefieldautocorrelationisjustthespectrum Beam splitter Inputpulse Delay Slowdetector Mirror Mirror E t E t t Okay sohowdowemeasureapulse V Wong I A Walmsley Opt Lett 19 287 289 1994 I A Walmsley V Wong J Opt Soc AmB 13 2453 2463 1996 Result Usingonlytime independent linearfilters completecharacterizationofapulseisNOTpossiblewithaslowdetector Translation Ifyou

《精编制作第八讲 超短脉冲强度测量PPT课件》由会员ahu****ng3分享，可在线阅读，更多相关《精编制作第八讲 超短脉冲强度测量PPT课件》请在金锄头文库上搜索。