考前复习参考0711

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1、Chapter1lightwavesphotonsmodes&statescoherencetemporalcoherencespatialcoherencecoherenceareacoherencevolumetemporalcoherencelengthtransversecoherencelengththermalradiationPlanck’sLawabsorptioninducedemissionspontaneousemission.transitionprobabilitytheEinsteincoefficientbasiceleme

2、ntsofalaserpopulationinversionthresholdcondition…Thenumberofmodes1.Inthevisiblepartofthespectrum(l=500nm;n=6x1014s-1),thenumberofmodesperunitvolumewithintheDopplerwidthofaspectralline(Dn=109s-1)is.2.Inthemicrowaveregion(l=1cm;n=3x1010s-1),thenumberofmodesperunitvolumewithinthetyp

3、icalDopplerwidthDn=105s-1is.3.IntheX-rayregion(l=1nm;n=3x1017s-1),thenumberofmodesperunitvolumewithinthetypicalDopplerwidthDn=1011s-1ofanX-raytransitionis.LightSourcesa)ExamplesofrealradiationsourceswithspectralenergydistributionsclosetothePlanckdistributionarethesun,thebrighttun

4、gstenwireofalightbulb,flashlamps,andhigh-pressuredischargelamps.b)Spectrallampswhichemitdiscretespectraareexamplesofnonthermalradiationsources.Inthesegas-dischargelamps,thelight-emittingatomsormoleculesmaybeinthermalequilibriumwithrespecttotheirtranslationalenergy,whichmeansthatt

5、heirvelocitydistributionisMaxwellian.However,thepopulationofthedifferentexcitedatomiclevelsmaynotnecessarilyfollowaBoltzmanndistributionandthereisgenerallyalsonothermalequilibriumbetweentheatomsandtheradiationfield.Theradiationmayneverthelessbeisotropic.c)Lasersareexamplesofnonth

6、ermalandanisotropicradiationsources.Theradiationfieldisconcentratedinafewmodes,andmostoftheradiationenergyisemittedintoasmallsolidangle.Thismeansthatthelaserrepresentsanextremeanisotropicradiationsource.InducedEmissiona)Inthethermalradiationfieldofa100wlightbulb,10cmawayfromthetu

7、ngstenwire,thenumberofphotonspermodeatl=500nmisabout10-8.Ifamolecularprobeisplacedinthisfield,theinducedemissionisthereforecompletelynegligible.b)Inthecenterspotofahigh-currentmercurydischargelampwithveryhighpressurethenumberofphotonspermodeisabout10-2atthecenterfrequencyofthestr

8、ongestemissionlineatl=253.6mm.Thisshowst