自适应光学波前传感技术.

自适应光学波前传感技术主要内容1、哈特曼夏克波前传感2、金字塔波前传感3、曲率波前传感都是非相干波前测量系统工作成绩哈特曼夏克波前传感EvolutionoftheHartmanntest–standarddevicesformeasuringwavefrontslopeerrors哈特曼夏克Onemethodfortestingalensormirroremploysanopaquemaskwithholesplacedbehindtheopticalelementundertest.Eachoftheholesactsasanaperture,andsincethelightpassingthroughthelensisconverging,theimageproducedisanarrayofspots.Withpropercalibration,thepositionofthespotsisadirectindicationofthelocalwavefronttiltateachhole,andthusisadescriptionofthelensquality.ThistestiscalledtheHartmanntest.Hartmanntest哈特曼夏克Shackplacedlensesintheholes,whichincreasedthelight-gatheringefficiencyofthemaskand,withthespotsfocused,reducedthedisturbingdiffractioneffectsoftheholes.Alensarrayforthispurposewasfirstmanufacturedin1971.Membersoftheastronomycommunitybegantousethissensorinthelate1970sfortestingoflargetelescopeoptics.SomeastronomersusethetermHartmann–Shack(orShack–Hartmann)wavefrontsensor,butmanyshortenittosimplyHartmannsensor.History哈特曼夏克TheHartmannwavefrontsensorisshowninbelowfigure.Thewavefrontisdividedbyamask,asintheclassicaltest,anarrayofgratings,oranarrayoftransmissivelenses.Eachofthebeamsinthesubaperturesisfocusedontoadetector.Todetectthepositionofthespot,variousformsofmodulation,detectorgeometry,andelectro-opticalprocessingareused.Foratmosphericturbulencecompensation,thelocalwavefronttiltmustbemeasuredaccuratelyineachsubapertureofsize.Todothis,thesubaperturemustbelargeenoughtoresolvetheisoplanaticpatch.Duringhighturbulence,issmallandanisoplanatismdegradestheprocess.Hardydiscussesdetailsofthislarge-versus-smallsubaperturetradeforvariousopticalandatmosphericparameters.Hartmannwavefrontsensor0r0r哈特曼夏克HartmannwavefrontsensorHartmannwavefrontsensingtechnique.AHartmannsensoriscomposedofanarrayoflensesforwavefrontdivisionandtypicallyaCCDarraywithmultiplepixelsusedforspotposition(wavefronttilt)determination.哈特曼夏克Ifthatsourceisanextendedobject,theshapeoftheobjectisconvolvedwiththesubaperturediffractionpatternonthequadcell.Intensityvariationcanseriouslydegradethemeasurementaccuracyofthecentroid.Toremovetheeffectsofextendedobjectsresolvedbythesubaperture,anopticalcorrelationcanbeused.VonderLuhesuggestedtheuseofanaddressableopticalmask,whosetransmissionisderivedfromtheimageofthereferencescene.TheHartmanndetectorarrayrecordsacross-correlationofthemaskandthesceneineachsubaperture.Eveniftheobjectremainsunresolved,theproblemsassociatedwithsubaperturehigher-orderaberrationswilldistortthepatternonthequadcellanddecreasetilt-measurementaccuracy.Extendedobject哈特曼夏克CorrelationTrackerFFWhenthewavefrontsourceisanextendedobject,acentroidmeasurement,likethatinaShack–Hartmannsensor,ismeaningless.Eachsubaperturecontainsasmallimageoftheentireobjectwiththeimageshiftedaccordingtosubaperturetilt.Toovercomethisproblem,oneimageischosenasareference.Thecross-covariancebetweeneachimageIiscalculatedbywherexisthe2-Dspatialcoordinate,δisthe2-Dimagedisplacement,andistheforwardandinverseFouriertransforms,and*indicatesthecomplexconjugate.Thismethodhasbeenappliedinsolartelescopeswherephotonsareplentiful,buttheobjectislarge.)(xIR哈特曼夏克Fordaytimeastronomywithlargebackgroundradiation,afield-of-viewshiftedShack–Hartmannwavefrontsensorcanbeused.Insolarimagingapplications,eachsubapertureseesanimageoftheextendedsource,thesun.Cross-correlationalgorithmsareusedtodeterminewavefronttilts,ratherthancentroids.Increasesinthespeedoftwo-dimensionaldetectorarraysandmicroprocessorshaveledtodevelopmentsthatutilizetheseadvantages.Thefirstsuchsystemtosuccessfullycompensateimagemotionofaground-basedsolartelescopewasthebreadboardcorrelationtrackerbuiltbytheSolarPhysicsGroupatLockheedPaloAltoResearchLaboratoryforimagemotioncompensationonaspacebornesolartelescope.Daytimeastronomy哈特曼夏克根据波前径向斜率测量原理,提出一种利用五棱镜扫描方法实现了新型自基准哈特曼波前传感器，其突出优点和特点是毋需任何外部信标或标准大平面反射镜提供工作基准。这对主动光学新技术的空间应用有重要意义。对大型天文望远镜光学系统裝校检测和大口径高精度抛物面反射镜以及平行光管等的检测也具有重要的应有价值。本方法的技术可行性强，容易实现；测量灵敏度与一般干涉法相当，但对光源的单色性和工作环境并无苛刻要求，因此便于推广应用。本方法由于采用了机械扫描采样方式，一次测量需时几分钟，所以不适用于以校正大气湍流为目的的自适应光学系统。自基准哈特曼波前传感器哈特曼夏克自基准哈特曼波前传感器),(图中五棱镜可单独沿被测物镜光瞳的半径方向平移,也可与五棱镜一起绕被测物镜的光轴转动。和的主截面彼此平行，并与光轴方向一致。当沿径向平移时可实现对被测物镜出射光束的离散采样。采样光束通过和后在相对被测物镜固定不动的CCD相机光敏面上生成一个艾利斑。测出处于光瞳面内不同位置时所对应的艾利斑质心坐标和相对偏移量的径向分量，由下式即可求得被测物镜出射波前斜率的径向分量1P2P1P2P1P1P2P1P哈特曼夏克理论分析和计算机仿真结果表明，在采样密度足够的情况下，根据已知波前径向斜率分量的离散采样值也完全可以以足够高的精度重构出原始波面的形状;如果径向斜率离散采样值包含有一定的随机误差，也仍能重构出精度与波前径向斜率采样精度相当的波前形状。用泽尼克径向斜率多项式作最小二乘拟合具体过程如下。对波面上每一点的径向斜率测量数据可分别写出自基准哈特曼波前传感器式中即为单位圆上点处第n项Zernike多项式的径向斜率值，也就是以Zernike多项式形式表示的基元波面的斜率值。为第1至第n项Zernike多项式的系数;为被测波面上各采样点处的径向斜率测量值;k和m分别为半径方向和圆周方向的采样点数。哈特曼夏克HartmannwavefrontsensorPrinciples:ThetelescopeimagepupilisreimagedonalensetarrayEachlensetproducesastarimageformingtheequivalentofaHartmannpattern,whichcanberecordedonaCCDThepositionofthecentroidofeachlensetimagecomparedtoareferencesuppliestheslopeofthewavefront(orwavefronttilt)atthelocationinobjectspacecorrespondingtothelensetCalibrationisdonewithareferenceplanewave哈特曼夏克HartmannwavefrontsensorAdvantages:CompactandruggedUsedforactive(samplingintervalofminutes)andadaptive(samplingintervalofmill