diffraction.ppt

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1、Chapter31DiffractionandPolarizationDiffractioneffectsoccurwheneverawavepassesthroughanaperture(缝隙)oraroundanobstacle.Theyareimportantinpracticalapplicationsofphysicalopticssuchasdiffractiongratings,x-raydiffraction,andholography(全息照相).diffraction(衍射)alternatingbrightanddarkfringes(明暗

2、交替的条纹)aperture(孔，缝隙)infinitesimal(无穷小的)emanate(发出，发射)Fresneldiffraction(菲涅尔衍射)Fraunhoferdiffraction(夫琅和费衍射)diffractiongrating(衍射光栅)holography(全息摄影术)KeyTerms:HuygensprincipleSingleslitgratingX-raydiffractionTypeofdiffractionphenomenadiffractionoflightphenomenaruleapplication“thebendin

3、goflightaroundanobstacle”31-1DiffractionPhenomenalightsourceobstaclescreen*S*SscreenobstaclescreenobstacleWhatisthedifferencebetweeninterferenceanddiffraction?Fresnel:finitedistanceinfinitedistancefinitedistancefinitedistanceinfinitedistancefinitedistanceFraunhofer:infinitedistancein

4、finitedistance31-2FresnelandFraunhoferDiffractionfOPAaBC*S1.experimentalapparatusLightfromentireslitarrivesatPinphase.Wegetacentralbrightband.lightintensityatPisdeterminedbythepathdifferencebetweenthetworaysemittedfromtheedgeoftheslit.diffractionangle.31-3FraunhoferDiffractionfromaS

5、ingleSlit222ABaC2.thecharacteristicsofofthediffractionpattern（P.703）1.Drawaseriesofparallelplane2.Considertworaysemittedfromthecorrespondingpointontheadjacentstrips.3.Sothelightwavesfromonestripcompletelycanceloutthelightwavesfromtheadjacentstrip.todivideBC(asin)intoseveralshort

6、segmentsofequallength/2,andsimultaneouslydividetheslitintoseveralnarrowstripsofequalwidth.2.Considertworaysemittedfromthecorrespondingpointontheadjacentstrips.Thepathdifferenceis/2,anddestructiveinterferenceoccurs.4.IthappensthatBCisdividedintotwostrips.BC=asin=2(/2),Adarkfringew

7、illbefound.Thinking:howabout4,6,8…strips?howabout3,5,7…strips?Caution:1)k0;2)strips?3)?;4)comparewithYoung’s…;2.thecharacteristicsofofthediffractionpattern222ABaCWidthofthesingle-slitpatternAngularspreadoftheCentralbrightbands:afIUsesmallangleapproximation:sin;tgWidthof

8、thecentralbr