北化大材料导论讲义第11章 光学性质(彩色版)

PositionPositionHEλX-radiationX-radiationMicrowaves微波无线电波γ-radiationUVIRRadiowaves10-610-311031061091012Wavelength(nm)可见光ε0=8.85×1012F/mμ0=4π×10-7H/mc=λνhisPlanck'shisPlanck'sconstant11.2光与材料的相互作用iReflectedbeamTransmittedbeamIRiRefractionIncidentbeamiReflectedbeamTransmittedbeamIRiRefractionIncidentbeamII0=IT+IA+IREnergyEmptyFilledEnergyElectronExcitationEnergyEmptyFilledEnergyElectronExcitation,E2E1E4E3E5金属中的电子跃迁PhotonabsorbedPhotonemittedFermienergyEnergyValenceBandConductionEnergyValenceBandConductionbandbandgapExcitedelectronHolePhotonemitted非金属中的电子跃迁PhotonabsorbedEgEnergyImpurityPhotonabsorbedEnergyImpurityPhotonabsorbedPhotonemittedhPhotonemittedPhotonemittedhPhotonemittedhPhononGeneratedhavingPhotonemittedhiIncidentbeamTransmittedbeam11.2.2折射cv折光指数r故与极化有关例题：将激光束引入折光指数为1.5的玻璃纤维，如何能使光线泄漏为最小？βααMaximumangle=90–α(a)(b) Solution Solution(a)设玻璃纤维处于空气(n=1)中,光子以60o的角度进入,β60o 如果入射光与纤维轴的夹角小于等于90-41.8=(c)(c)如果纤维浸于水(n=1.333)中,则:为避免发生透射，入射角必须小于90-62.7=27.3o。入射IncidentbeamReflectedbeam入射Incidentbeami反射iiVacuum(orair)Glass折射RefractionbeamFresnel’sformula反射的最小化主反射反射的最小化主反射PrimaryreflectedwaveSecondaryreflectedwave二级反射入射IncidentwaveλSubstrate(n2>n1)基材Coating(n1>1)涂层空气Air(n=1)入射光Incidentlight实际表面的反射特征反射topographySpecularreflectiontopography实际表面True实际表面Truesurface弥散散射平均表面Averagesurface反射极图反射极图入射光θ“光滑”表面粗糙表面(a)(b)入射光I理想粗糙表面Iθ=I0入射光I理想粗糙表面Iθ=I0cosθ例题例题:计算可见光谱中光子完全透射和完全吸收的临界Solution可见光最短波长λ(min)约为0.4μm,则吸收可见光的最大能这说明能隙大于3.1eV的非金属材料不能吸收光线，如果材料是纯的，则为无色透明。吸收机理产生跃迁的条件：hchν>Eorhν>Eor>E吸收不仅与介质本质有关，也与路径长短有关吸收不仅与介质本质有关，也与路径长短有关I'T=I'0e_βxβ为吸收系数（单位mm-1由材料本质所决定可见光最大波长λ可见光最大波长λ(max)约为0.7μm，发生吸收的最小能EXAMPLEEXAMPLE设计一滤板，使能至少透过95%Zn的KαX光。以铝为材料，其吸收系数为1.08×104m-1，忽略反射。Solution由公式I=Ie_βxln(0.95)=_0.051=_1.08×104xT0AbsorptionAbsorptionReflectedbeamIncidentbeamTransmittedbeamI0(1-R)2e-βlI0(1-R)2e-βlReflectedbeamI0R(1-R)e-βlEXAMPLEEXAMPLE一材料的反射率为0.15，吸收系数为1×104m-1.设计一挡板使只有1%的光线透过.Solution0.01=(1_0.15)2exp(_1×104x)=0.01384=exp(_104x)ln(0.01384)=_4.28=_104xx=4.28×10_4m=0.428m透明与半透明透明与半透明入射光弥散反射Diffusereflection特征反射Specularreflection弥散透射特征透射DiffusetransmissionSpeculartransmissionIncidentlightIncidentlightrayPore(n=1)Glassorceramic(n>1)Scatteredlightray氧化铝的颜色90Transmittance(%)VioletGreenOran90Transmittance(%)BlueYellowRed80Sappire7060Rubby50400.30.40.50.60.70.80.91.0Wavelength,λ(μm)11.3.1X-rayfluorescentanalysis(X萤光分IncomingelectronE1+E2+E3+E4+E5=E0ααβαCopperKλ=0.154nmKλ=0.139nmwhereK=1s2levelL=2s2p6levelM=2s2p6d10levelIntensityofemittedradiationEnergyCharacteristicCharacteristicpeaksαKβContinuousradiationLow-energystimulusHigh-energystimulusLKαWavelength11.3.2LUMINESCENCE(11.3.2LUMINESCENCE(发光)Fluorescence(萤光)reemissionoccursfortimesmuchlessthanonesecond再发射时间短于1秒Phosphorescence(磷光)forlongertimes再发射时间较长金属光子Photone激励StimulusValencee激励StimulusValenceband价带eNoEλverylongConductionbandeValenceband价带萤光材料光子PhotonConductionbandeValenceband价带萤光材料光子PhotonEStimulus激励e磷光材料光子λ==TrapEEeStimulusTrapEEeStimulusConductionbandValenceband价带激励Electroluminescence电致发光 light-emittingdiodes(LEDs)n-typep-typesilvercontactElectroluminescence电致发光 light-emittingdiodes(LEDs)n-typep-typesilvercontactI+11.3.3激光LightAmplificationbyStimulatedEmissionofRadiation.FlashlampRubyPowersourceCoherentbeamEnergySpontaneousdecay(nonradiative,EnergySpontaneousdecay(nonradiative,phononemission)M亚稳态Spontaneousandstimulatedemission激光G氙灯入射光基态(Cr)激发态E反射前晶体中部反射后(d)(e)激发Cr原子基态Cr原子(a)(b)(c)完全镀银部分镀银ExcitedelectronsExcitedelectronsPhotonemissionHolesValencebandConductionbandRecombinedexcitedelectronandhole部分镀银完全镀银ConductionbandValencebandENewholeNewholeConductionbandConductionbandValencebandValencebandNewexcitedelectronValencebandConductionbandValenceband(f)Conductionbandconductionband)11.3.4光导性Incidentphotonconductionband)11.3.4光导性Incidentphotonhν≥ENWWWWWW E(bottomof O(topofvalenceband)VoltageproducedVoltageproduced太阳能电池e-n-typehh+p-typeEg11.3.5光导纤维Electrical/ConverterInputSignalFiberOpticCableOutputSignalOptical/ElectricalDecoderEncoderOpticalRepeaterConverterIntensityIntensityTime(b)DigitalencodingTimeIntensityIntensityTime(b)DigitalencodingTime(a)CoaxialdesignofcommercialopticalfibersCladdingCoatingIntensityIntensi