光学外文文献及翻译

学号2013211033昆明理工大学专业英语专业光学姓名辜苏导师李重光教授分数导师签字日期2015年5月6日研究生部专业英语考核年级：2013级学院：理学院姓名：辜苏学号：2013211033专业：光学文献原文：Title：Phase-shiftingdigitalholographyinimagereconstructionAbstract:Aphase-shiftingdigitalholographyschemedevelopedtoinvestigateinternaldefectsinartworksisdescribed.Phase-shiftingisutilizedtoobtainaclearreconstructedobjectwavefromaroughsurfacetexture.Areverse-transformalgorithmisemployedtoreconstructtheobjectwaveonitsoriginalpositionofunknowndistanceortheimagingpositionfromtheobjectwaveinformationontheholographicplane.Togettheclearestreconstructiontheexactregistrationoftheunknowndistanceisdeterminedbyapplyingtheintensitysumastheauto-focusingfunction.Thespatialresolutionofthereconstructionimageisalsoinvestigatedforavarietyofaffectingfactors.Laboratoryresultsofreconstructionimagesunderdeformationarepresented.Keywords：holographicinterferometry,digitalholography,phase-shiftingtechnique,reverse-transformalgorithm,auto-focusingfunction,spatialresolution.1IntroductionDifferentmethodsofholographicinterferometryrelatedtechniqueshavebeenusedeffectivelyfordefectvisualisationinartworkdiagnosis.Physicalreconstructionofrecordedwavefieldsthoughisoflimitedapplicabilityforon-fieldorremoteapplicationsusuallyrequiredinartconservationenvironments.DigitalcounterpartsexplorednowadaystorecordtheinterferencebetweenanobjectanditsreferenceonCCDandreconstructtherecordnumericallyarebettersuitedforfielduse.Howevertheydonotprovidetheessentialspatialresolutionforcleanobjectreconstructionanddefectdetection,bothcriticalinartworkdiagnosticassessment.Towardsthisgoal,thisstudyaimsatovercomingtheabovelimitationsandexpandingtheuseofsuchtechniquesinthefieldofartworksconservation.Aprincipalproblemindigitalholographyofartworksistoobtainaclearreconstruction.Toaccomplishthisthefollowingproblemsshouldbeaddressed:(1)needofaproperalgorithmforthereconstructionofrecordedimages,(2)removaloreliminationofspecklenoiseinthereconstructedimageandphasemap,(3)determinationoftheactualregistrationdistance,(4)improvementofspatialresolutionofthereconstructedimage.Thefirsttwoproblemsisreferredtoasreconstructionalgorithms.Thesealgorithmscanbedividedintotwocategories.OnerealizesreconstructionfromasinglehologramasforexampletheFresnelalgorithmandtheconvolutionalgorithm.Suchalgorithmsonlyrequireasinglehologramandaresuitablefordynamicmeasurements,butthezero-orderspeckleandtheeffectofthereferencebeamarenotthoroughlyremoved.Thesecondcombinesthephase-shiftingtechniqueanddigitalholographytogethertoproduceimagereconstruction.Itsimportantadvantageistheabilitytoeliminatecompletelytheeffectofthereferencebeam,soitcangetaclearreconstructedimage.Indigitalholographyofartworks,mostoftheinvestigatedobjectshaveacoarsesurfaceandbigslopechangingsothatthespatialphase-shiftingtechniqueisunsuited.Therefore,evenifthetemporalphase-shiftingtechniqueisimproperfordynamictesting,itisappliedwidely.Inthisapproach,thefirststepusesaphase-shiftingtechniquetorecordtheobjectwaveontheholographicplate.Thenthereconstructionobjectwavecanbecalculatedatitsoriginalorimagingposition.Towardsthisgoalweproposeareconstructionalgorithmbasedonareverse-transformalgorithm,whichaccordswiththenotionofthedigitalholographyinprincipleandalsoproducesgoodreconstructionresults.Inthereconstructionprocess,iftheregistrationdistanceusedhasabigdifferencewithitsactualvalue,thereconstructedimagewillbefuzzy.Inafirstapproximation,thisdistancecanbemeasuredintheopticaltestingsystemorestimatedbytheclarityobtainedinthereconstructedimage,butsuchapproacheslackaccuracyandstandardization.Thispaperproposedamethodtodeterminetheexactregistrationdistance,whichappliestheintensitysumofthereconstructionimageastheevaluatingfunctioninordertodeterminethetruevalue.Improvingthereconstructionspatialresolutionisanimportantproblemworthaddressing.2Reconstructionbasedonphase-shiftingdigitalholographyTherelationshipbetweentheobject,hologramandreconstructedimageisshownFig.1,wherexandydenotethecoordinatesoftheobjectplane,andthehologramplane,andxandythereconstructionplane,distheregistrationdistance,disthereconstructiondistance.Indigitalholography,therecordingCCDisplacedonthe-planeinordertoregisterthehologramx,ywhentheobjectliesinthex-yplane.Forthereconstructionoftheinformationoftheobjectwave,phase-shiftingdigitalholographyincludestwosteps:(1)gettingobjectwaveonhologramplane,and(2)reconstructingoriginalobjectwave.2.1GettinginformationofobjectwaveonhologramplateDoingphaseshiftingN-1timesandcapturingNholograms.Supposingtheinterferogramafterk-1timesphase-shiftingis]),(cos[),(),(),,(kkbaI（1）Phasedetectioncanapplytwokindsofalgorithms:synchronousphasedetectionalgorithms[9]andtheleastsquaresiterativealgorithm[10].Thefour-stepalgorithminsynchronousphasedetectionalgorithmisincommonuse.Thecalculationequationis)2/3,,(),,()]2/,,()0,,([2/1),(iIIiIIE2.2Reconstructingoriginalobjectwavebyreverse-transformalgorithmObjectwavefromtheoriginalobjectspreadsfront.Theprocessinghasexactandcleardescriptionandexpressioninphysicsandmathematics.Byphase