Ocean-Optics-光纤光谱仪.ppt
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OceanOpticsSpectrometersSimplesolutionsforIntricateproblems,Spectroscopyis,Spectroscopyisthescienceandmeasurementofemission&absorptionspectraoflightandotherformsofelectromagneticradiationandhowmaterials(matter)interactswithradiantenergy,Spectrumisaviewofradiantenergydispersedintoitswavelengthconstituents,LightandMatter,Absorbance,Transmission,Reflection,Refraction,Lightenterstheopticalfiberandisefficientlytransmittedtothespectrometer.Onceinthespectrometer,thedivergentlightemergingfromtheopticalfiberiscollimatedbyasphericalmirror.Thecollimatedlightisdiffractedbyaplanegrating,andtheresultingdiffractedlightisfocusedbyasecondsphericalmirror.Animageofthespectrumisprojectedontoa1-dimensionallinearCCDarray,andthedataistransferredtoacomputerthroughanA/Dconverter.,OpticalBenchFeatures,Grating,Detector,CrossedCzerny-Turneropticalpath,DetectorCoating,CollectionLens,SlitBlockingfilterModeStripper,OrderSortingFilter,TheFundamentalBalanceofSpectrometerConfiguration,Resolution,Sensitivity,SpectralRange,Everythingbeginshere,Spectrometersareselected.,BydetectortypeByopticalbenchtypeByconfigurationtypeByapplication/function,DetectorTypes,SilinearCCDarrayBack-thinnedareaCCDSilinearphotodiodearrayInGaAslineararrayCMOS(OEMonly),Sony2048-element,Toshiba3648-element,QE/MAYAback-thinnedDetector,WhatisaCCD?
CCDstandsforcharge-coupleddevice.ACCDisadetectormadeonasiliconwafer.Duetothephysicalnatureofsilicon,photonsoflightthathititgenerateelectronsinthesilicon.ThejoboftheCCDistocollecttheseelectronsinitslightbuckets(calledpixels)duringthelengthoftheexposuretolight.Themorelightfallingonaparticularlightbucketorpixel,themoreelectronsthatpixelwillcontain.Thebucketsthentransfertheirelectrons(thinkwaterbucketbrigade)outtotheCCDcontroller(whichcontainstheelectronicstocontroltheCCD)andontothecomputer.Thecomputerregeneratestheimageandwenowseethespectra,CCDPIXELBUCKETS,LightEnergy,PHOTONS,CCDOperation,PhotonsstrikingPixelscauseChargetoleaktoGroundDarkcurrentChargeleaksalittleanywayExposurelastsfordurationofintegrationperiodQuantumefficiency,PixelWells,PHOTONCharge,Pixels,Ground,Atendofintegrationperiod,remainingchargeindicateshowmanyphotonsweredetectedA/DconvertschargetoCounts,Saturated!
Nochargeleft,sonoresponsetofurtherphotons,Counts,Pixels,Saturated!
Quantumefficiency(QE)isameasureofhowwellaspecificsensorrespondstodifferentwavelengthsoflight.ThehighertheQE,themoresensitiveaCCDwillbeataparticularwavelength.Thequantumefficiency(QE)offront-illuminatedCCDisaround40%.Thismeans40outof100incidentphotonsweredetected.Back-illuminatedCCDshaveapeakquantumefficiencyupwardsof90%-90outof100photonsofacertainwavelengtharedetected!
Ontheotherhand,photographicfilmandthehumaneyehaveapeakQEofabout10%.,Infront-illuminatedCCDs,lightmustpassthroughthepolysilicongatestructurelocatedabovethephotosensitivesiliconlayercalledthe“depletionlayer.”,Inback-thinneddevices,alsoknownasback-illuminatedCCDs,theincidentphotonfluxdoesnothavetopenetratethepolysilicongatesandisabsorbeddirectlyintothesiliconpixels.,FrontIlluminated,BackIlluminated,BackThinningTheetchingawayofsiliconfromthebacksideofaCCD.Thinningisdoneinalargebathofacid.Thedeviceismountedonasupportandisthenagitated.Waxisusedtomountthedevicetoitssupport,sincetheaciddoesnotattackwax.Whentheacidhaseatenawayacertainamountofsilicon,theCCDthatwasonce0.010thickbecomes0.0005thick!
Whatisthedifference?
OpticalBenchFeatures,Grating,Detector,CrossedCzerny-Turneropticalpath,DetectorCoating,CollectionLens,SlitBlockingfilterModeStripper,OrderSortingFilter,SpectrometerPerformanceCriteria,Signal-to-NoiseRatio(Detector)SensitivityResolution,SmallestdetectablesignalchangeisafunctionoftheS:
NforthespectrometerWecanaccuratelydetectasignalthatis2xtheS:
NTheS:
NdependsonlyonthedetectorchoiceTheS:
Ndoesnotdependonopticalbenchconfiguration,SpectrometerSensitivity,EntranceOpticsandResolution,FixedSlitsNomovingpartstoalignorcomelooseFixedopticalresolutionvalueCanuselargerfiberstocollectmorelightNoSlits(usingthefiber)SlitwidtheasilychangedAllthelightfromthefiberisusedFiberdiameterdeterminesopticalresolution,OpticalResolution,wavelength,real,FWHM,perfect,SpectrometerResolution,Measuredasfull-widthathalf-maximum(FWHM)forapeak,Wavelength,Intensity,nm,TheFundamentalBalanceofSpectrometerConfiguration,Resolution,Sensitivity,SpectralRange,Everythingbeginshere,SpectrometerResolution,Dependson:
OpticalBenchdesignBigger=betterresolution(worsespectralrange)Sizeofd