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1、Reflected-light–polarizationcontrast(POL)Suitableforsurfaceswithstructureswhichchangethestateofpolarizationduringreflection,e.g.structuregrainsinsamplesofore.Theilluminatinglight(1)hitsapolarizer(2,P)firstandisimaged,linearlypolarized,onthesamplesurface(5).Behindtheb
2、eamsplitter,ithitstheanalyzer(6,A),whichallowsonlythedepolarizedportionofthelighttoreachthetubelens(7).Asintransmittedlight,anoptionallambdaplate(6a,λ)enablesthechangeoverfromgreycontrasttocolorcontrast.Whenobjectivesofaverylowmagnificationareused,aso-calledAntiflexc
3、ap(arotatableλ/4-Platteinfrontoftheobjective)permitsotherwiseunavoidablereflectiontobealsoeliminatedfrom“dark”samplesurfaces.Theinnerstructureofthesespherulitesisbarelyvisibleinreflected-lightbrightfield.Thestructureinthepolishedironsamplebecomesclearlyvisibleinpolar
4、izationcontrast.Transmittedlight–polarizationcontrastInthismethod,polarizedlightisused;itconsistsoflightwaveswhichallfeaturethesamedirectionofvibration,i.e.whicharelinearlypolarized.Thisvery“ordered”lightisgeneratedbypolarizerswhichfilteroutaprivilegedplanefromthesta
5、tisticalconfusionofvibrationdirectionsprevailinginnaturallight.Itisanimportantfactthattwofiltersofthistypedonotletanylightpasswhentheyarearrangedonebehindtheotherinthebeampathatanangleof90°toeachother.Thefirstfiltersortsoutthevibrationdirectionsinsuchawaythatthesecon
6、dfiltercannotletpassthisveryselection.Thesecondfilteriscalled“analyzer”,sinceitallowstheprivilegeddirectionofthefirstfilter–called“polarizer”–tobechecked.Theappropriatearrangementisrelativelyeasytoimplementinthemicroscope.Thepolarizer(1)onthecondenser–neartheaperture
7、diaphragm–ensuresthatthespecimen(3)isilluminatedwithlinearlypolarizedlightviathecondenser.Theanalyzer(5),arrangedatanangleof90°tothepolarizer(1),islocatedbehindtheobjective.Thetubelens(6)formstheintermediateimage(7).Ifnospecimenisonthemicroscopestage–oronlyanempty,cl
8、eanmicroscopeslide–theimagewillremaincompletelydark.Whenilluminated,manyspecimensturnthevibrationdirectionofthepolarizedlightoutoft
