Multi-Color Coronagraph Experiment in a Vacuum Testbed with a Binary Shaped Pupil Mask

摘要

Weconductedanumberofmulti-color/broadbandcoronagraphexperimentsusingavacuumchamberandabinary-shapedpupilmask,whichinprincipleshouldworkatallwavelengths,inthecontextoftheresearchanddevelopmentofastellarcoronagraphtoobserveextra-solarplanets(exoplanets)directly.TheaimofthisworkistodemonstratethatsubtractionofthePointSpreadFunction(PSF)andmulti-color/broadbandexperimentsusingabinary-shapedpupilmaskcoronagraphwouldhelptoimprovethecontrastinobservationsofexoplanets.Acheckerboardmask,akindofbinary-shapedpupilmask,wasused.Weimprovedthetemperaturestabilitybyinstallingthecoronagraphopticsinavacuumchamber,whilecontrollingthetemperatureoftheopticalbench,andcoveringthevacuumchamberwiththermalinsulationlayers.Activewavefrontcontrolwasnotappliedinthiswork.WeevaluatedhowmuchthePSFsubtractioncontributedtothehigh-contrastobservationbysubtractingimagesobtainedthroughthecoronagraph.Wealsocarriedoutmulti-color/broadbandexperimentsinordertodemonstrateamorerealisticobservationusingSuperluminescentLightEmittingDiodes(SLEDs)withcenterwavelengthsof650nm,750nm,800nm,and850nm.Acontrastof2.3$$ imes$$10$$^{-7}$$wasobtainedfortherawcoronagraphicimageandacontrastof1.3$$ imes$$10$$^{-9}$$wasachievedafterPSFsubtractionwithaHe-Nelaserat632.8nmwavelength.Thus,thecontrastwasimprovedbyaroundtwoordersofmagnitudefromtherawcontrastbysubtractingthePSF.Weachievedcontrastsof3.1$$ imes$$10$$^{-7}$$,1.1$$ imes$$10$$^{-6}$$,1.6$$ imes$$10$$^{-6}$$,and2.5$$ imes$$10$$^{-6}$$atthebandsof650nm,750nm,800nm,and850nm,respectively,inmulti-color/broadbandexperiments.Theresultsshowthatthecontrastwithineachofthewavelengthbandswassignificantlyimprovedcomparedwiththenon-coronagraphicoptics.WedemonstratedthatPSFsubtractionispotentiallybeneficialforimprovingthecontrastofabinary-shapedpupilmaskcoronagraph;thiscoronagraphproducesasignificantimprovementincontrastwithmulti-color/broadbandlightsources.