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1、IntensityAutocorrelation1DPhaseRetrievalagainSingle-shotautocorrelationTheAutocorrelationandSpectrumAmbiguitiesThird-orderAutocorrelationInterferometricAutocorrelationMeasuringUltrashortLaserPulsesI:AutocorrelationWhy?ThedilemmaThegoal:measuringtheintensityandphasevs.time(orfr
2、equency)TheSpectrometerandMichelsonInterferometer1DPhaseRetrievalTime(t)Intensity(I)Todeterminethetemporalresolutionofanexperimentusingit.Todeterminewhetheritcanbemadeevenshorter.Tobetterunderstandthelasersthatemitthemandtoverifymodelsofultrashortpulsegeneration.Tobetterstud
3、ymedia:thebetterweknowthelightinandlightout,thebetterweknowthemediumwestudywiththem.Tousepulsesofspecificintensityandphasevs.timetocontrolchemicalreactions.Tounderstandpulse-shapingeffortsfortelecommunications,etc.Becauseit’sthere.Whymeasureanultrashortlaserpulse?Asamole
4、culedissociates,itsemissionchangescolor(i.e.,thephasechanges),revealingmuchaboutthemoleculardynamics,notavail-ablefromthemerespectrum,oreventheintensityvs.time.ExcitationtoexcitedstateEmissionGroundstateExcitedstateImportantpointaboutclaimsofthegenerationofinterestingscientif
5、icobjects“Ifyouhaven’tmeasuredit,youhaven’tmadeit!”WayneKnox(1957-)Director,InstituteofOptics,UniversityofRochester,Rochester,NYUSAWayneKnoxInordertomeasureaneventintime,youneedashorterone.Tostudythisevent,youneedastrobelightpulsethat’sshorter.Butthen,tomeasurethestrobelightpu
6、lse,youneedadetectorwhoseresponsetimeisevenshorter.Andsoon…So,now,howdoyoumeasuretheshortestevent?PhotographtakenbyHaroldEdgerton,MITTheDilemmaUltrashortlaserpulsesaretheshortesttechnologicaleventsevercreatedbyhumans.Usinganultrashortpulse,youcanmeasurealmostanyevent—providedt
7、hatyourpulseisshorter.Sohowdoyoumeasurethepulseitself?Youmustusethepulsetomeasureitself.Butthatisn’tgoodenough.It’sonlyasshortasthepulse.It’snotshorter.Techniquesbasedonusingthepulsetomeasureitselfhavenotsufficed.Blurrypicturemeasuredusinganinsufficientlyshortevent.Theelectri
8、cfieldcanbewritten:IntensityPhaseAlternatively,versusfrequenc