大学物理课件 光学第三十一章衍射

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1、Chapter31DiffractionandPolarization1.DiffractionofLight2.DiffractionGratings3.X-RayDiffraction4.PolarizedLight31-1.DiffractionofLight(P703)1.Diffraction(衍射)byasingleslitscreenscreenshadowWhentheslitiswide,lighttravelsinstraightlines.Whentheslitgetsnarrow,lightprod

2、ucesadiffractionpatternonthescreen.Whenmonochromatic(单色)lightfromadistantsourcepassesthroughanarrowslitorobstacle——producesadiffractionpattern(光能绕过障碍物的边缘传播形成具有明暗相间的衍射图样)iscalleddiffractionoflight(P703).Conditionofdiffraction:thewidthofaslit(dimensionofabarrier)iss

3、imilartothewavelengthoflight.(a～λ)Recalling:Hugens-Fresnel’sprinciple波传到的任何一点都是子波的波源，各次级子波在空间某点的相干叠加，就决定了该点波的强度。Themethodfordiscussingthelocationofdiffractionpatternforasingle-slitdiffractioniscalledFresnel’shalf-wave-zonemethod(半波带).2.Locatingthediffractionbands(

4、P704)slitaLscreenL·PBSa*OAδffEAlensdoesn’tproduceadditionallight-pathdifference.PathdifferenceofA→P&B→P:asinmaxasinmax(i)0，0thecentralbright(中央明纹)(ii)asinlthefirstdarkfringeTwohalf-wave-zonescanbegotten,andPisthefirstdarkfringe(apairsofrays:outofph

5、ase)Inasingle-slitdiffractionexperiment,darkfringesareproducedwherethepathlengthdifferences(asin)betweenthetopandbottomraysareequaltol,2l,3l,…3(iii)asinl2thefirstbrightfringescreen屏幕PaConclusions:mlm1,2,3,darkasinl(2m1)m1,2,3,bright2oppositet

6、otheconditionsofinterferencepatternForthecentralbrightfringe:asin0i.e.lasinlsintanAngularwidth(角宽度):l2201alLinear-width:x2ftan2f01a:半角宽度1whenax0Forthe1st-orderdarkfringe,x1asinatanalfflPositionofthe1thdarkx1afringe一级暗纹坐标Similarly,fo

7、rthe2nd-orderdarkfringe,2flxPositionofthe2nddarkfringe2aWidthofeachorderbrightfringe:fl1xx0——halfofthecentralwidth.a2其他明纹宽度为中央明纹宽度的一半Example:Aslit1.00mmwideisilluminatedbylightofl=589nm.Weseeadiffractionpatternonascreen3.00maway.Whatisthedistancebetweenthefi

8、rsttwodiffractionminimaonthesamesideofthecentraldiffractionmaximum?Solution:Usingtheconditionofminimaofdiffraction:asinmlxftanandxftan1122Thesepar