超快光学 第02章 概述

《超快光学 第02章 概述》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、TheGenerationofUltrashortLaserPulsesTheimportanceofbandwidthMorethanjustalightbulbLasers,lasermodes,andmode-lockingMakingshorterandshorterpulsesPulse-pumpingQ-switchinganddistributed-feedbacklasersPassivemode-lockingandthesaturableabsorberKerr-lensingandTi:SapphireActivemode-lockingOthermode-lockin

2、gtechniquesLimitingfactorsCommerciallasersProf.RickTrebinoGeorgiaTechwww.frog.gatech.eduButfirst:theprogresshasbeenamazing!YEARNd:glassS-PDyeDyeCWDyeNd:YAGDiodeNd:YLFCr:YAGCr:LiS(C)AFEr:fiberCr:forsteriteTi:sapphireCPMw/CompressionColorCenter1965197019751980198519901995Dye2000SHORTESTPULSEDURATION1

3、0ps1ps100fs10fs2005Nd:fiberTheshortestpulsevs.year(fordifferentmedia)Continuousvs.ultrashortpulsesoflightAconstantandadelta-functionareaFourier-Transformpair.Continuousbeam:Ultrashortpulse:Irradiancevs.timeSpectrumtimetimefrequencyfrequencyLongvs.shortpulsesoflightTheuncertaintyprinciplesaysthatthe

4、productofthetemporalandspectralpulsewidthsisgreaterthan~1.LongpulseShortpulseIrradiancevs.timeSpectrumtimetimefrequencyfrequencyFormanyyears,dyeshavebeenthebroadbandmediathathavegeneratedultrashortlaserpulses.Ultrafastsolid-statelasermediahaverecentlyreplaceddyesinmostlabs.Solid-statelasermediahave

5、broadbandwidthsandareconvenient.LaserpowerButalightbulbisalsobroadband.Whatexactlyisrequiredtomakeanultrashortpulse?Answer:AMode-lockedLaserOkay,what’salaser,whataremodes,andwhatdoesitmeantolockthem?Lightbulbs,lasers,andultrashortpulsesStimulatedemissionleadstoachainreactionandlaseremission.E

6、xcitedmediumIfmanymoleculesinamediumareexcited,onephotoncanbecomemany.Thisistheessenceofthelaser.ThefactorbywhichaninputbeamisamplifiedbyamediumiscalledthegainandisrepresentedbyG.Usually,additionallossesinintensityoccur,suchasabsorption,scat-tering,andreflections.Ingeneral,thelaserwilllaseif,inarou

7、ndtrip:TotalGain>TotalLossThiscalledachievingThreshold.TheLaserAlaserisamediumthatstoresenergy,surroundedbytwomirrors.Theoutputmirrorispartiallyreflectingandsoletssomelightout.Alaserwilllaseifthebeamincreas