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1、Thegoal:measuringtheintensityandphasevs.time(orfrequency)Theways:TheSpectrometerandMichelsonInterferometerScanningAutocorrelationSingle-shotautocorrelationTheAutocorrelationandSpectrumThird-orderAutocorrelationInterferometricAutocorrelationMeasuringUltrashort
2、LaserPulsesI:AutocorrelationE(t)E(t–t)Inordertomeasureaneventintime,youneedashorterone.Tostudythisevent,youneedastrobelightpulsethat’sshorter.Butthen,tomeasurethestrobelightpulse,youneedadetectorwhoseresponsetimeisevenshorter.Andsoon…So,now,howdoyoumeasurethe
3、shortestevent?PhotographtakenbyHaroldEdgerton,MITTheDilemmaUltrashortlaserpulsesaretheshortesttechnologicaleventsevercreatedbyhumans.It’sroutinetogeneratepulsesshorterthan10-13secondsinduration,andresearchershavegeneratedpulsesonlyafewfs(10-15s)long.Suchpulse
4、shavemanyapplicationsinphysics,chemistry,biology,andengineering.Youcanmeasureanyevent—aslongasyou’vegotapulsethat’sshorter.Sohowdoyoumeasurethepulseitself?Youmustusethepulsetomeasureitself.Butthatisn’tgoodenough.It’sonlyasshortasthepulse.It’snotshorter.Techni
5、quesbasedonusingthepulsetomeasureitselfhavenotsufficed.Todeterminethetemporalresolutionofanexperimentusingit.Todeterminewhetheritcanbemadeevenshorter.Tobetterunderstandthelasersthatemitthemandtoverifymodelsofultrashortpulsegeneration.Tobetterstudymedia:thebet
6、terweknowthelightinandlightout,thebetterweknowthemediumwestudywiththem.Tousepulsesofspecificintensityandphasevs.timetocontrolchemicalreactions:“Coherentcontrol.”Tounderstandpulse-shapingeffortsfortelecommunications,etc.Becauseit’sthere.Whymeasureanultrashortl
7、aserpulse?Asamoleculedissociates,itsemissionchangescolor(i.e.,thephasechanges),revealingmuchaboutthemoleculardynamics,notavail-ablefromthemerespectrum,oreventheintensityvs.time.ExcitationtoexcitedstateEmissionGroundstateExcitedstateExp’tTheoryLinearLinearorn
8、onlinearmediumMeasuringtheintensityandphaseofthepulsesintoandoutofamediumtellsusasmuchaspossibleaboutthelinearandnonlineareffectsinthemedium.StudyingMediabyMeasuringtheIntensityandPhaseof