用迈克尔逊干涉仪空气的折射率PB07210137昝涛一、实验目的用分离的光学元件构建一个迈克尔逊干涉仪。通过降低空气的压强测量其折射率。二、仪器和光学元件光学平台；HeNe激光；调整架，35x35mm；平面镜，30x30mm；磁性基座；分束器50:50；透镜，f=+20mm；白屏；玻璃容器，手持气压泵，组合夹具，T形连接，适配器，软管，硅管三、实验原理借助迈克尔逊干涉仪装置中的两个镜，光线被引进干涉仪。通过改变光路中容器内气体的压强，推算出空气的折射率。IftwoWaveshavingthesamefrequency,butdifferentamplitudesanddifferentphasesarecoincidentatonelocation,theysuperimposetoTheresultingcanbedescribedbythefollowlng:withtheamplitude(1)andthephasedifferenceInaMichelsoninterferometer,thelightbeamissplitbyahalf-silveredglassplateintotwopartialbeams(amplitudesplitting),reflectedbytwomirrors,andagainbroughttointerferencebehindtheglassplate.Sinceonlylargeluminousspotscanexhibitcircularinterferencefringes,theIightbeamisexpandedbetweenthelaserandtheglassplatebyalensL.IfonereplacestherealmirrorM3withitsvirtualimageM3/,,Whichisformedbyreflectionbytheglassplate,apointPofthereallightsourceappearsasthepointsP/,andP"ofthevirtuallightsourcesLlandL2·Duetothedifferentlightpaths,usingthedesignationsinFig.2,图2thephasedifferenceisgivenby:（2）isthewavelengthofthelaserljghtused.Accordingto(1),theintensitydistributionforis(3)Maximathusoccurwhenisequaltoamultipleof,hencewith(2)；m=1，2，…..(4)i.e.therearecircularfringesforselected,fixedvaluesofm,andd,sinceremainsconstant(seeFig.3).IfonealtersthepositionofthemovablemirrorM3(cf.Fig.1)suchthatd,e.g.,decreases,accordingto(4),theciroularfringediameterwouldalsodiminishsincemisindeeddefinedforthisring.Thus,aringdisappearseachtimedisreducedby.Ford=0theciroularfringepatterndisappears.IfthesurfacesofmirrorsM4andM3arenotparallelinthesenseofFig.2,oneobtainscurvedfringes,whichgraduallychangeintostraightfringesatd=0.空气衍射系数的确定Tomeasurethediffractionnofair,anair-filledcellwithplane-parallelboundariesisused.ThediffractionindexnofagasisalinearfunctionofthepressureP.ForpressureP=0anabsolute...
