材料導(dǎo)論第十一章光學(xué)性質(zhì)PositionEHl光的傳播m0=

4p10-7H/m

0=8.85

1012F/m真空磁通率真空電容率qiqrTransmittedbeamIncidentbeamqiReflectedbeamI0RefractionITIRAbsorptionIA11.2光與材料的相互作用

透射反射折射吸收入射qiqrRefractionbeamGlassVacuum(orair)IncidentbeamqiReflectedbeam11.2.1反射入射反射折射反射機(jī)理DEDEDEDE金屬非金屬無透明的金屬IncidentlightSpecularreflectionDiffusereflectionTruesurfacetopographyAveragesurface入射光特征反射彌散散射實(shí)際表面平均表面實(shí)際表面的反射入射光入射光I0qI=I0cosq“光滑”表面粗糙表面(a)(b)反射極圖理想粗糙表面qiqrTransmittedbeamIncidentbeamI0IT11.2.2折射透射入射折光指數(shù)

絕大多數(shù)材料mr

1故與極化有關(guān)折射機(jī)理(b)為防止光線泄漏，b角至少應(yīng)為90:如果入射光與纖維軸的夾角小于等于90-41.8=48.2，光線就完全被反射。Maximumangle=90–aab=90

為避免發(fā)生透射，入射角必須小于90-62.7=27.3。Maximumangle=90–aab=90

(c)如果纖維浸于水(n=1.333)中,則:(1)電子極化生熱11.2.4吸收與透射吸收機(jī)理(2)電子躍遷顯示顏色產(chǎn)生躍遷的條件：例題:計(jì)算可見光譜中光子完全透射和完全吸收的臨界帶隙Solution這說明帶隙大于3.1eV的非金屬材料不能吸收光線，如果材料是純的，則為無色透明?？梢姽庾疃滩ㄩL

(min)約為0.4

m,則吸收可見光的最大帶隙Eg(max)為：可見光最大波長

(max)約為0.7

m，發(fā)生吸收的最小帶隙Eg(min)為：如果帶隙＜1.8eV，則全部可見光被吸收，材料不透明如果帶隙在1.8和3.1eV之間，則材料顯示顏色躍遷后的幾種可能DEDE1DE2DE1DE2光子光子光子聲子吸收不僅與介質(zhì)本質(zhì)有關(guān)，也與路徑長短有關(guān)b為吸收系數(shù)（單位mm-1），由材料本質(zhì)所決定IncidentlightrayPore(n=1)Glassorceramic(n>1)Scatteredlightray內(nèi)部孔穴造成的散射I0RIncidentbeamI0TransmittedbeamI0(1-R)2e-bxReflectedbeamReflectedbeamI0R(1-R)e-bxI0(1-R)Absorption

反射光吸收反射光透射光入射光I0(1-R)e-bxEXAMPLE設(shè)計(jì)一濾板，使能至少透過95%Zn的KaX光。以鋁為材料，其吸收系數(shù)為1.08104m-1，忽略反射Solution由公式故鋁板厚度應(yīng)小于等于0.0047mm11.3光學(xué)性質(zhì)的應(yīng)用Ka

l=0.154nmDE=1.2910-15JKb

l=0.139nmDE=0.1510-15JLa

l=1.336nm

DE=1.4310-15JwhereK=1s2levelL=2s2p6levelM=2s2p6d10levelCopperKLM銅CharacteristicpeaksContinuousradiationHigh-energystimulusLaKbKalswlIntensityofemittedradiationLow-energystimulusEnergyWavelengthShortwavelengthlimitFluorescence(螢光)reemissionoccursfortimesmuchlessthanonesecondPhosphorescence(磷光)forlongertimes11.3.2LUMINESCENCE(發(fā)光)再發(fā)射時(shí)間較長再發(fā)射時(shí)間短于1秒PhotonStimulusValencebandNoEg

lverylonge－e－金屬激勵(lì)光子價(jià)帶螢光材料StimulusPhotonConductionbandValencebande－e－Eg激勵(lì)光子價(jià)帶TrapEdEgStimulusConductionbandValencebande－e－e－磷光材料激勵(lì)光子價(jià)帶松弛時(shí)間，材料常數(shù)撤除光源后的時(shí)間初始光強(qiáng)時(shí)間t光強(qiáng)例題：為電視機(jī)的藍(lán)色選擇一種材料藍(lán)光波長為4.510-5cm，其光子能量為SOLUTION查表找到CaWO4，光子波長為4.310-5cm，松弛時(shí)間為410-6s，正好作為藍(lán)光材料，但不能產(chǎn)生磷光。又找到ZnS的Eg為5.67110-19J，可提供一個(gè)(5.671-4.422)10-19=1.24910-19J的中間帶隙于是選ZnS為雜質(zhì)材料，可以產(chǎn)生磷光。5.6714.422CaWO4ZnSEg-EdEgElectroluminescencelight-emittingdiodes(LEDs)Isilvercontactn-typep-type+電致發(fā)光電子＋空穴hnIncidentphotonhn

Eg11.3.3光導(dǎo)性n-typep-typeVoltageproducede－h(huán)+太陽能電池

LightAmplificationbyStimulatedEmissionofRadiation.CoherentbeamFlashlampRubyPowersource11.3.4激光電弧燈反射前晶體中部反射后基態(tài)Cr原子激發(fā)Cr原子(a)(b)(c)(d)(e)完全鍍銀部分鍍銀HolesExcitedelectronsValencebandPhotonemissionConductionbandEg(a)ValencebandConductionbandRecombinedexcitedelectronandhole(b)完全鍍銀部分鍍銀ValencebandConductionbandNewexcitedelectronNewhole(c)ValencebandConductionband(d)ValencebandConductionband(e)ValencebandConductionband(f)InputSignalEncoderElectrical/OpticalConverterRepeaterOptical/ElectricalConverterDecoderOutputSignalFiberOpticCable11.3.5光導(dǎo)纖維輸入信號(hào)電光轉(zhuǎn)換復(fù)制光電轉(zhuǎn)換輸出編碼解碼DigitalencodingIntensityTime(a)IntensityTime(b)數(shù)字編碼CoaxialdesignofcommercialopticalfibersCoreCladdingCoating同軸光纜IntensityIntensityIntensityTimeInputpulseTimeInputpulseTimeInputpulseIntensityIntensityIntensityTimeOutputpulseTimeOutputpulseTimeOutputpulse(c)(b)(a)完Visiblespectrum4x10-7m5x10-7m6x10-7m7x10-7mg-Raysx-RaysUltravioletVisibleInfraredMicrowaveRadio,TVEnergy(eV)Frequency(Hz)Wavelength(m)10-1010010410210610810-410-610-810-210201022101010810610410181016101210141km1A1nm1mm1mm1m10-1410-1210-1010-810-610-410-21001021040.4mm0.5mm0.6mm0.7mmVisiblespectrumwavelength

一些透明材料的折光指數(shù)

MaterialAverageIndexofRefractionCeramicsSilicaglass 1.458Borosilicate(Pyrex)glass 1.47Soda-limeglass 1.51Quartz(SiO2) 1.55Denseopticalflintglass 1.65Spinel(MgAl2O4) 1.72Periclase(MgO) 1.74Corundum(Al2O3) 1.76PolymersPolytetrafluoroethylene 1.35Polymethylmethacrylate 1.49Polypropylene 1.49Polyethylene 1.51Polystyrene 1.600.20.30.40.50.60.70.81.01.52.02.53.0ReflectedTransmittedvisibleFractionofradiantenergyWavelength(mm)1.00.80.60.40.20AbsorbedIncidentwavePrimaryreflectedwaveSecondaryreflectedwavel1/4l

入射主反射二級(jí)反射空氣Substrate(n2>n1)基材Air(n=1)Coating(n1>1)涂層反射的最小化電子極化能量吸收速度降低折射電子躍遷11.2.1作用機(jī)理吸收后再釋放E5E3E4E2E1EnergyDE=E4-E2=hn42電子躍遷

頻率為n42的入射光子DEPhotonemittedDEFermienergyEnergyFilledstatesEmptystatesPhotonabsorbed金屬中的電子躍遷DEPhotonemittedExcitedfreeelectronDEEgPhotonabsorbedEnergyConductionbandValencebandBandgapHole非金屬中的電子躍遷DEPhotonabsorbedEnergyConductionbandValencebandBandgapImpurityle