raman-spectroscopy拉曼光谱.ppt

1、Biomedical Raman SpectroscopyJason T.MotzHarvard Medical School and The Wellman Center for PhotomedicineMassachusetts General Hospital11 April 20062A New Type of Secondary RadiationC.V.Raman and K.S.Krishnan,Nature,121(3048):501-502,March 31,1928If we assume that the X-ray scattering of the unmodifi

2、ed type observed by Prof.Compton corresponds to the normal or average state of the atoms and molecules,while the modified scattering of altered wave-length corresponds to their fluctuations from that state,it would follow that we should expect also in the case of ordinary light two types of scatteri

3、ng,one determined by the normal optical properties of the atoms or molecules,and another representing the effect of their fluctuations from their normal state.It accordingly becomes necessary to test whether this is actually the case.The experiments we have made have confirmed this anticipation,and

4、shown that in every case in which light is scattered by the molecules in dust-free liquids or gases,the diffuse radiation of the ordinary kind,having the same wave-length as the incident beam,is accompanied by a modified scattered radiation of degraded frequency.The new type of light scattering disc

5、overed by us naturally requires very powerful illumination for its observation.In our experiments,a beam of sunlight was converged successively by a telescope objective of 18 cm.aperture and 230 cm.focal length,and by a second lens was placed the scattering material,which is either a liquid(carefull

6、y purified by repeated distillation in vacuo)or its dust-free vapour.To detect the presence of a modified scattered radiation,the method of complementary light-filters was used.A blue-violet filter,when coupled with a yellow-green filter and placed in the incident light,completely extinguished the t

7、rack of the light through the liquid or vapour.The reappearance of the track when the yellow filter is transferred to a place between it and the observers eye is proof of the existence of a modified scattered radiation.Spectroscopic confirmation is also available.Some sixty different common liquids

8、have been examined in this way,and every one of them showed the effect in greater or less degree.That the effect is a true scattering,and secondly by its polarisation,which is in many cases quire strong and comparable with the polarisation of the ordinary scattering.The investigation is naturally mu

9、ch more difficult in the case of gases and vapours,owing to the excessive feebleness of the effect.Nevertheless,when the vapour is of sufficient density,for example with ether or amylene,the modified scattering is readily demonstrable.3Professor Sir C.V.Raman1888-1970The Nobel Prize in Physics 1930f

10、or his work on the scattering of light and for the discovery of the effect named after himFirst photographed Raman spectraBangalore,India4The Raman Effect:Inelastic Scatteringhih(i-R)hi3210 S13210 S0EnergyVirtual Level Rayleigh Raman(inelastic)(elastic)Scattering ScatteringInelastic ScatteringEnergy

11、 transferred from incident light to molecular vibrationsEmitted light has decreased energy(iR)difference in energy5Some Vibrations in BenzeneBreathingChubby CheckerKekule6Evolution of Raman Spectroscopy19281960Minor experimental advances1960Invention of laser expands scope experiments1980s:rapid tec

12、hnological advancesFourier Transform spectroscopyCharge Coupled Device(CCD)detectorsHolographic and dielectric filtersNear-Infrared(NIR)lasersLate 1980s1990sBiomedical investigationsAdvanced dispersive spectrometers2000 In vivo applicationOptical fiber probesNon-linear spectroscopy7OutlineThe Raman

13、EffectTheoryTechniques&ApplicationsBiomedical Raman SpectroscopyHistoryExcitation wavelength selectionAdvantages of Raman spectroscopyInstrumentationLaboratoryClinical:optical fiber probes Case Study:AtherosclerosisDisease backgroundImpact of Raman spectroscopyFrontiers8Classical Raman PhysicsIntera

14、ction between electric field of incident photon and moleculeElectric field oscillating with incident frequency vi:Induces molecular electric dipole(p):Proportional to molecular polarizability,ease with which the electron cloud around a molecule can be distortedPolarization results in nuclear displac

15、ement9Classical Raman PhysicsFor small distortions,polarizability is linearly proportional to the displacementResultant dipole:Rayleigh ScatteringAnti-Stokes RamanStokes Raman103210 n1Auto-IRRayleighStokesAnti-StokesNIRFluorescenceAbsorptionScattering Raman ScatteringFluorescenceEnergyVirtual Levels

16、210 n0210 n1Photo-Molecular InteractionsAnti-StokesStokesRayleighScatteringE=hR11Classical Raman PhysicsRaman scattering occurs only when the molecule is polarizableRaman intensity 4Classical dipole radiationStokes shifted Raman is more intense than anti-Stokes by Boltzmann factor:Consistent with other scattering phenomena,often reported in terms of cross-section(cm2),or probability of scattering:density of moleculesdz:pathlength12Characteristics of Raman ScatteringVery weak effectOnly 1 in 107