Laser Far-Field Focal Spot Measurement Method Based on Multistep Phase Retrieval

被引：2
|
作者：
Chen Xiaoyi [1 ,2 ]
Duan Yaxuan [1 ]
Wang Zhengzhou [1 ]
Yuan Suochao [1 ]
Da Zhengshang [1 ]
机构：
[1] Chinese Acad Sci, Xian Inst Opt & Precis Mech, Adv Opt Instrument Res Dept, Xian 710119, Shaanxi, Peoples R China
[2] Univ Chinese Acad Sci China, Beijing 100049, Peoples R China
来源：
CHINESE JOURNAL OF LASERS-ZHONGGUO JIGUANG | 2022年 / 49卷 / 07期
关键词：
measurement; laser; far-field focal spot; phase retrieval; chirp-z transform; ALGORITHM;
D O I：
10.3788/CJL202249.0704002
中图分类号：
O43 [光学];
学科分类号：
070207 ; 0803 ;
摘要：
Objective The intensity distribution of the laserfar-field focal spot is an essential index for measuring the qualityoflaserbeams Itisalsothemainparameterthatreflectsthelaserbeam????sabilitytoentertheholeintheinertialconfinementfusionsystem Howtomeasuretheintensitydistributionofthelaserfar-fieldfocalspotwithhighprecisiondeterminestheevaluationresultoftheoverallperformanceofthelasersystem Itisofgreatguidingsignificanceinthetheoreticaldesignstage developmentstage orfinalstageofpracticaloperationofthelaserdevice Directmeasurementmethodsoffar-fieldfocalspotsincludethelong-focal-lengthimagingarraycamera andschlierenmethods Thelong-focal-lengthlensimagingmethodislimitedbythelinearresponserangeofthedetector Thearraycameramethodusesawedge whichintroducesadditionalopticalpathdifferenceandwaveaberration Theschlierenmethodmeasuresthemainlobeandsidelobeofthefocalspotseparatelywhichiseasilyaffectedbythemeasuredenvironmentandnoise TheShack-Hartmannwavefrontmeasurementisanindirectmeasurementmethodandcausesthelossofmiddleandhighfrequencyinformationduetoitsfrequencyresponsecharacteristics Toachieveahigh-precisionmeasurementoffar-fieldfocalspot thispaperproposesamethodbasedonmultistepphaseretrievalformeasuringfar-fieldfocalspots Theoreticallyafocalspotreconstructionmodelbasedonmultistepphaseretrievalisderived Then thechirp-ztransformCZTisintroducedtosolvetheproblemofunder-samplingincalculatingfocalspots ComparedwiththetraditionalfastFouriertransformFFTwithzero-paddingusingCZTtocalculatethefocalspotavoidscalculationredundancyTheproposedmethodhasa higher measurement accuracy of a focal spot than the traditional long-focal-length lens imaging method MethodsTheproposedlaserfar-fieldfocalspotmeasurementmethodbasedonmultistepphaseretrievalcanbedividedintotwoparts First themultistepphaseretrievalmethodisusedtoobtainthenear-fieldcomplexamplitudeoftheobjectplane Then itissubstitutedintothereconstructedmodelofthelaserfar-fieldfocalspotandusesCZTtoobtaintheintensitydistributionofthelaserfar-fieldfocalspot Meanwhile consideringthatthemultistepphaseretrievalmethodwillintroducedistanceerrorsduetothetranslationofthedetector thequantumgeneticalgorithmQGAisusedtooptimizethedistanceerrors Thelaserfar-fieldfocalspotreconstructionalgorithmbasedonmultistepphaseretrievalispresented Weusethetheoreticalsimulationtoanalyzetheinfluenceofscanningstepsizeandthenumberofdetectionpositionsontheconvergenceoftheproposedmethod Thus theoptimalscanningstepsizeandthenumberofdetectionpositionsaredetermined Furthermore averificationdevicebasedonapurephaseliquidcrystalspatiallightmodulatorSLMissetupexperimentallytoverifytheeffectivenessoftheproposedmethod Wealsocomparetheexperimentalresultsoftheproposedmethodandtraditionallong-focal-lengthlensimagingmethod ResultsandDiscussionsInthesimulation thelasernear-fieldcomplexamplitudeoftheobjectplaneiseffectivelyretrieved TheretrievedandtheoreticalfocalspotshavethesamedistributionofmainlobeandsidelobeinthefocalspotFig7ComparedwithCZT thefocalspotcalculatedusingFFTisunder-sampled andthedetailedinformationinthefocalspotislostFig7ThepowerinthebucketPIBcurvesoftheoreticalandretrievedfocalspotsarecompletelycoincidentintheintegralareaoftheentirebucketradiusFig7Intheexperiment themainlobedistributionbetweenthetheoreticalandretrievedfar-fieldfocalspotsisconsistentFig9However theopticalcomponentsintroducesmallaberrations andthesurfacesoftheseopticalcomponentswillinterferewitheachother resultinginasmalldifferencebetweenthedistributionofsidelobesforthetheoreticalandretrievedfar-fieldfocalspotsFig9Inthetraditionallong-focal-lengthlensimagingmethod theintroductionoflensaberrationsandinsufficientdynamicresponserangeoftheCCDleadtolargererrorsinthemainlobeandsidelobeoffocalspotsthanthoseinthetheoreticalfocalspotFig9Thecorrelationcoefficientbetweentheretrievedfocalspotusingtheproposedmethodandthetheoreticalfocalspotis0 9976 However thecorrelationcoefficientbetweenthemeasuredfocalspotusingthelong-focal-lengthlensimagingmethodandthetheoreticalfocalspotis0 9477 Thisalsoconfirmsthatthemeasurementaccuracyoffocalspotsusingtheproposedmethodismuchhigherthanthatofthelong-focal-lengthlensimagingmethod ConclusionsThispaperproposesalaserfar-fieldfocalspotmeasurementmethodbasedonmultistepphaseretrieval Theeffectivenessofthemethodisverifiedthroughtheoreticalsimulationandexperiments Thetheoreticalsimulationresultsshowthatthenear-fieldcomplexamplitudeandfar-fieldfocalspotoflasersareeffectivelyretrieved AdditionallythePIBcurvesofthetheoreticalandretrievedfocalspotsarecoincident Moreover theexperimentalresultsshowthattheprofileoftheretrievedphaseisconsistentwiththatofthetheoreticalphaseloadedusingSLM Therefore theretrievedandtheoreticalfocalspotshavethesamedistributionofthemainlobe However thereisasmalldifferenceinthesidelobesbecausetheopticalcomponentsintroducesmallaberrations andthesurfacesoftheseopticalcomponentswillinterferewitheachother Thesidelobeinformationoffocalspotsusingthelong-focal-lengthlensimagingmethodislostbecauseofthelimiteddynamicresponserangeinCCD Therefore theproposedmethodhashigherprecisionoflaserfar-fieldfocalspotthanthetraditionallong-focal-lengthlensimagingmethod The results show that the proposed method can provide a technical meansfor the high-precision measurement of laser far-field focal spots
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