raman-spectroscopy拉曼光谱.ppt

raman-spectroscopy拉曼光谱.ppt

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BiomedicalRamanSpectroscopyJasonT.MotzHarvardMedicalSchoolandTheWellmanCenterforPhotomedicineMassachusettsGeneralHospital11April20062ANewTypeofSecondaryRadiationC.V.RamanandK.S.Krishnan,Nature,121（3048）:

501-502,March31,1928IfweassumethattheX-rayscatteringoftheunmodifiedtypeobservedbyProf.Comptoncorrespondstothenormaloraveragestateoftheatomsandmolecules,whilethemodifiedscatteringofalteredwave-lengthcorrespondstotheirfluctuationsfromthatstate,itwouldfollowthatweshouldexpectalsointhecaseofordinarylighttwotypesofscattering,onedeterminedbythenormalopticalpropertiesoftheatomsormolecules,andanotherrepresentingtheeffectoftheirfluctuationsfromtheirnormalstate.Itaccordinglybecomesnecessarytotestwhetherthisisactuallythecase.Theexperimentswehavemadehaveconfirmedthisanticipation,andshownthatineverycaseinwhichlightisscatteredbythemoleculesindust-freeliquidsorgases,thediffuseradiationoftheordinarykind,havingthesamewave-lengthastheincidentbeam,isaccompaniedbyamodifiedscatteredradiationofdegradedfrequency.Thenewtypeoflightscatteringdiscoveredbyusnaturallyrequiresverypowerfulilluminationforitsobservation.Inourexperiments,abeamofsunlightwasconvergedsuccessivelybyatelescopeobjectiveof18cm.apertureand230cm.focallength,andbyasecondlenswasplacedthescatteringmaterial,whichiseitheraliquid（carefullypurifiedbyrepeateddistillationinvacuo）oritsdust-freevapour.Todetectthepresenceofamodifiedscatteredradiation,themethodofcomplementarylight-filterswasused.Ablue-violetfilter,whencoupledwithayellow-greenfilterandplacedintheincidentlight,completelyextinguishedthetrackofthelightthroughtheliquidorvapour.Thereappearanceofthetrackwhentheyellowfilteristransferredtoaplacebetweenitandtheobserverseyeisproofoftheexistenceofamodifiedscatteredradiation.Spectroscopicconfirmationisalsoavailable.Somesixtydifferentcommonliquidshavebeenexaminedinthisway,andeveryoneofthemshowedtheeffectingreaterorlessdegree.Thattheeffectisatruescattering,andsecondlybyitspolarisation,whichisinmanycasesquirestrongandcomparablewiththepolarisationoftheordinaryscattering.Theinvestigationisnaturallymuchmoredifficultinthecaseofgasesandvapours,owingtotheexcessivefeeblenessoftheeffect.Nevertheless,whenthevapourisofsufficientdensity,forexamplewithetheroramylene,themodifiedscatteringisreadilydemonstrable.3ProfessorSirC.V.Raman1888-1970TheNobelPrizeinPhysics1930forhisworkonthescatteringoflightandforthediscoveryoftheeffectnamedafterhimFirstphotographedRamanspectraBangalore,India4TheRamanEffect:

InelasticScatteringhih（i-R）hi3210S13210S0EnergyVirtualLevelRayleighRaman（inelastic）（elastic）ScatteringScatteringInelasticScatteringEnergytransferredfromincidentlighttomolecularvibrationsEmittedlighthasdecreasedenergy（iR）differenceinenergy5SomeVibrationsinBenzeneBreathingChubbyCheckerKekule6EvolutionofRamanSpectroscopy19281960Minorexperimentaladvances1960Inventionoflaserexpandsscopeexperiments1980s:

rapidtechnologicaladvancesFourierTransformspectroscopyChargeCoupledDevice（CCD）detectorsHolographicanddielectricfiltersNear-Infrared（NIR）lasersLate1980s1990sBiomedicalinvestigationsAdvanceddispersivespectrometers2000InvivoapplicationOpticalfiberprobesNon-linearspectroscopy7OutlineTheRamanEffectTheoryTechniques&ApplicationsBiomedicalRamanSpectroscopyHistoryExcitationwavelengthselectionAdvantagesofRamanspectroscopyInstrumentationLaboratoryClinical:

opticalfiberprobesCaseStudy:

AtherosclerosisDiseasebackgroundImpactofRamanspectroscopyFrontiers8ClassicalRamanPhysicsInteractionbetweenelectricfieldofincidentphotonandmoleculeElectricfieldoscillatingwithincidentfrequencyvi:

Inducesmolecularelectricdipole（p）:

Proportionaltomolecularpolarizability,easewithwhichtheelectroncloudaroundamoleculecanbedistortedPolarizationresultsinnucleardisplacement9ClassicalRamanPhysicsForsmalldistortions,polarizabilityislinearlyproportionaltothedisplacementResultantdipole:

RayleighScatteringAnti-StokesRamanStokesRaman103210n1Auto-IRRayleighStokesAnti-StokesNIRFluorescenceAbsorptionScatteringRamanScatteringFluorescenceEnergyVirtualLevels210n0210n1Photo-MolecularInteractionsAnti-StokesStokesRayleighScatteringE=hR11ClassicalRamanPhysicsRamanscatteringoccursonlywhenthemoleculeispolarizableRamanintensity4ClassicaldipoleradiationStokesshiftedRamanismoreintensethananti-StokesbyBoltzmannfactor:

Consistentwithotherscatteringphenomena,oftenreportedintermsofcross-section（cm2）,orprobabilityofscattering:

densityofmoleculesdz:

pathlength12CharacteristicsofRamanScatteringVeryweakeffectOnly1in107