QUANTUM Fluctuation in small laser USC.pdf

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1、QuantumfluctuationsinsmalllasersA.F.J.LeviEPFLColloquium,July29,20091ThelaserdiodeCoherentlightLaserdiode,LDIthLight,LIncoherentlightLightemittingdiode,LEDCurrent,I•Photonsexperiencenon-linearthresholdbehaviortransitioningfromdisorderedlight(spontaneousemission)toorderedlight(st

2、imulatedemission)withincreasingpumpcurrent•Activevolume300x0.14x0.8m3=34x10-12cm-3=34m3•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!9FluctuationsdescribedbyLangevinequationsCarrierrecombinationrateeSinglemode,singlefrequencylaserdioderateequationsinthepresenceofnoise,FBRadiativerecombinationrated

8、nIIInjectioncurrentGsnF(t),Equationgover