固体材料的宏观光学性质

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1、第四章固体材料的宏观光学性质OverviewThestudyoftheopticalpropertiesofmaterialsisahugefieldandwewillonlybeabletotouchonsomeofthemostbasicpartsSowewillconsidertheessentialpropertiessuchasabsorption/reflection/transmissionandrefractionThenwewilllookatotherphenomenalikeluminescenceandfluorescenceFinallywewi

2、llmentionapplications,inparticularopticalfibresandlasersNatureoflightLightisanelectromagneticwave:withavelocitygivenbyc = 1/(00)=3x108m/sInviewofthis,itisnotsurprisingthattheelectricfieldcomponentofthewaveshouldinteractwithelectronselectrostaticallyhttp://www.astronomynotes.com/light/e

3、manim.gifManyoftheelectronicpropertiesofmaterials,informationonthebonding,materialcompositionetc.wasdiscoveredusingspectroscopy,thestudyofabsorbedoremittedradiationevidenceforenergylevelsinatomsevidenceforenergybandsandband-gapsphotoelectriceffectGeneraldescriptionofabsorptionBecauseofcon

4、servationofenergy,wecansaythatI0=IT+IA+IRIoistheintensity(W/m2)ofincidentlightandsubscriptsrefertotransmitted,absorbedorreflectedAlternativelyT+A+R=1whereT,A,andRarefractionsoftheamountofincidentlightT=IT/I0,etc.Somaterialsarebroadlyclassedastransparent:relativelylittleabsorptionandreflec

5、tiontranslucent:lightscatteredwithinthematerial(seeright)opaque:relativelylittletransmissionhttp://www.tekano.pwp.blueyonder.co.uk/tekano/translucent.jpgIfthematerialisnotperfectlytransparent,theintensitydecreasesexponentiallywithdistanceConsiderasmallthicknessofmaterial,xThefallofintens

6、ityinxisIsoI=-a.x.Iwhereistheabsorptioncoefficient(dimensionsarem-1)Inthelimitofx0,wegetThesolutionofwhichisI = I0exp(–x)Taking“ln”ofbothsides,wehave:whichisknownasLambert’sLaw(healsohasaunitoflightintensitynamedforhim)Thus,ifwecanplot-ln(I)againstx,weshouldfindfromthegradientDep

7、endingonthematerialandthewavelength,lightcanbeabsorbedbynuclei–allmaterialselectrons–metalsandsmallband-gapmaterialsATOMICABSORPTIONHowthesolidabsorbstheradiationdependsonwhatitis!Solidswhichbondionically,showhighabsorptionbecauseionsofoppositechargemoveinoppositedi