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1、QuantumfluctuationsinsmalllasersA.F.J.LeviEPFLColloquium,July29,20091ThelaserdiodeCoherentlightLaserdiode,LDIthLight,LIncoherentlightLightemittingdiode,LEDCurrent,I•Photonsexperiencenon-linearthresholdbehaviortransitioningfromdisorderedlight(spontaneousemission)toorderedlight(st
2、imulatedemission)withincreasingpumpcurrent•Activevolume300x0.14x0.8m3=34x10-12cm-3=34m3•I=3mA,=2x107,=105,=10-4,7psphotoncavityround-thtrip•Existingmean-fieldtheories(rateequationsandGaussiannoise-Langevin)appliestotheselargesystems2Askasimplequestion:Whendophotonsknowt
3、heyareinalaser?3Whendophotonsknowtheyareinalaser?•NOTonecavityround-trip•Cavityformationtakesmanyphotonroundtrips•AdiabaticallydecoupleelectrondynamicsinexperimentbyusinglargecavityLDLED4Whendophotonsknowtheyareinalaser?•NOTonecavityround-trip•Cavityformationtakesmanyphotonround
4、trips•SpectralpurityLDLED5Askasimplequestion:Howdophotonfluctuationsbelowthresholdimpactlasingemission?6FluctuationsenhancelightoutputbelowIth•ExperimentallyLDcompareLEDandLDusingSAMEgeometryandactiveregion•ARcoatLDtomakeLED•Landau-Ginzburgphasetransitionanalogyforbulkwithbelow-
5、thresholdLEDfluctuationsintothelasingstate•Intensityfluctuationsscaleas1/(T/T–1)C•Experimentally=1.04,T=301.4KC7Fluctuationsandcarrierpinning•ExperimentallycompareLEDandLDusingSAMEgeometryandactiveregion•ARcoatLDtomakeLED•CarriernumbernfromL(spontaneousWemission)•Fluctuationsi
6、nphotonssremovecarriersbelowthresholdandcontributetothetemperaturedependenceoflaserdiodethresholdcurrent,Ith•Thereisacontribution,I,tothethresholdcurrentIflth8Summarysofar:Photonfluctuationsinlargelaserdiodes:EnhancelasingemissionbelowthethresholdcurrentRemovecarriersbelowthethr
7、esholdcurrentContributetothetemperaturedependenceofthelaserdiodethresholdcurrentPhotonfluctuationsareimportant!9FluctuationsdescribedbyLangevinequationsCarrierrecombinationrateeSinglemode,singlefrequencylaserdioderateequationsinthepresenceofnoise,FBRadiativerecombinationrated
8、nIIInjectioncurrentGsnF(t),Equationgover