High Accuracy Laser Power and Energy Meter Calibration

1 Page 1 NAT'LINST.OFSTAND&TECH NISI PUBLICATIONS AlllDbbMt3fl3 NISTSpecialPublication250-62 NISTMeasurementServices High-AccuracyLaserPowerand EnergyMeterCalibrationService DavidLivigni NationalInstituteofStandardsandTechnology... Open at page → 2 Page 2 rhe NationalInstituteofStandardsandTechnologywasestablishedin1988byCongressto"assistindustryin thedevelopmentoftechnology ...neededtoimproveproductquality,tomodernizemanufacturingprocesses, toensureproductreliability . .... Open at page → 3 Page 3 NISTSpecialPublication250-62 NISTMeasurementServices High-AccuracyLaserPowerand EnergyMeterCalibrationService DavidLivigni OptoelectronicsDivision ElectronicsandElectricalEngineeringLaboratory NationalInstituteofStandard... Open at page → 4 Page 4 Certaincommercialentities,equipment,ormaterialsmaybeidentifiedinthis documentinordertodescribeanexperimentalprocedureorconceptadequately.Such identification isnotintendedtoimplyrecommendation orendorsementbythe NationalI... Open at page → 5 Page 5 Contents 1.INTRODUCTION 1 2.fflGH-ACCURACYLASERPOWERANDENERGYMETERCALIBRATIONSYSTEM 2 2.1CalibrationSystemOverview 2 2.2CalibrationPhilosophy 4 2.3ParameterSpecificationforEnd-UserUncertaintyAssessment 5 3.SYSTEMDESIGNAN... Open at page → 6 Page 6 5.1.3Receiveralignment 57 5.1.4Electricalcalibration 57 5.1.5Electricalheatinginequivalence 57 5.1.6OtherLOCRuncertainties 58 5.2UncertaintyoftheAppliedPower 59 5.2.1Relativeaperturetransmittance 59 5.2.2Measurementrepea... Open at page → 7 Page 7 H.lWindowTransmittanceMeasurement:PhilosophyandTechnique 123 H.2TransmittanceMeasurement:UncertaintyAnalysis 125 H.3ExampleCalculationofTransmittance 128 APPENDIX!. Center-Weighted SpatialUncertainty 129 APPENDIX!. Estim... Open at page → 8 Page 8 ListofIllustrations Figure1.Calibrationsystemoverview 2 Figure2.Currentconfigurationoftliehigh-accuracycalibrationsystem 7 Figure3.High-accuracycalibrationsystemlaboratorytableandenclosure 9 Figure4.High-accuracycalibrat... Open at page → 9 Page 9 High-AccuracyLaserPowerandEnergyMeterCalibrationService DavidJ.Livigni NationalInstituteofStandardsandTechnology Boulder,CO80303 Thisdocumentdescribesthehigh-accuracy laserpowerandenergymetercalibration serviceprovidedby... Open at page → 11 Page 11 1.INTRODUCTION Wehavebuiltacalibrationsystemtomeettheindustry'sneedforveryhigh-accuracymeasurementsof laserpowerandenergy,atvarious(selected)wavelengths.Thesystememploysacommercialcryogenic radiometerastheprimarystandard... Open at page → 12 Page 12 2.HIGH-ACCURACYLASERPOWERANDENERGYMETERCALIBRATIONSYSTEM Thegoalofthehigh-accuracycalibrationserviceistoprovidelaserpowerandenergymetercalibrations forthemostdemandingcustomers, vv-ithlowuncertainty(<0.1%),performedinast... Open at page → 13 Page 13 providingthedirectsubstitutionofthestandardwiththeDUT.TheLOCRprimarystandardandmultiple DUTscanbeplacedontheplatform,allowingcalibrationofmorethanoneDUTatatime.Eachdetector isalignedsothatwhenitismovedintothebeam,itsentr... Open at page → 14 Page 14 laboratory.Theweatherstationlogsairtemperature,pressure,andhumidity,sonoadditionalsensorsare neededfortheseenvironmentalparameters. Calibrations atmultiplepowerlevelscanbeusedtodeterminetheDUT'spowerlinearitywithahigh de... Open at page → 15 Page 15 aseparateuncertaintyforDUTquantization isdeterminedbyvisualanalysisofthereadingsacquired duringtheDUT'scalibration. 2.3ParameterSpecificationforEnd-UserUncertaintyAssessment Customerswhodesirehigh-accuracycalibrationstyp... Open at page → 16 Page 16 asingledominantnarrowspectralline(narrowerthan15THz,about10nmat633nm)ismeasuredwith aprecisionwavelengthmeter.Somelasersproducemultiplespectrallines;theirspectraareusually describedinthetextbystatingthedistancebetweenthe... Open at page → 17 Page 17 RS-232Bus LOCR Computer o < o o H 00 Weather %Station AirTemperature BarometricPressure IEEE-488Bus ii Floppy 19Disk ProcessControl Computer DataAnalysis Computer CalibrationReport Printer DataArchive onFileServer =3 oo... Open at page → 18 Page 18 3.SYSTEMDESIGNANDIMPLEMENTATION Whileconceptuallysimple,performingcalibrationswiththelowestpossibleuncertainty isdifficult. Manysourcesofsmalluncertainties,typicallyconsiderednegligibleinlessaccuratecalibrationsystems, a... Open at page → 19 Page 19 HEPAFilter AluminumFrame Enclosure,with SlidingBlackPanels AirIonizer OpticalSource Breadboard LabTable LOCR LevelingPosts ScatteredLight Shield Detector Breadboard Figure3.High-accuracy calibrationsystemlaboratorytablea... Open at page → 20 Page 20 flowingoutoftheventilationhoodisexchangedwithfreshairfromthebuilding'sventilationsystem,so thegasconcentrations returntonormalatmosphericvaluesafteraboutanhour.Asecondindependent ventilationsystemwithflexibleductswasalso... Open at page → 21 Page 21 TestDetectorElectronics Figure4.High-accuracycalibrationsystem'slaboratorytablelayout. resultingunidirectionalreproducibility isapproximately±0.04mm,whichisnegligiblecomparedtothe alignmentuncertainty,whichisusuallyafewt... Open at page → 22 Page 22 3.1.4Gasandcryogenhandlingsystems :BothliquidandgaseousHeand areusedintheHigh- AccuracyCalibrationSystem.ThecryogenicliquidsareusedtocooltheLOCR.TheN,gasisused duringLOCRpre-coolingandasadrygasforventingandgeneralcleanin... Open at page → 23 Page 23 Attenuator2 Iris1 Mirror1 Rail2 LaserPower ControllerModulator Lens1 PinholeMount Rail1 InterferenceFilters Attenuator 1 1550nmLaser (FiberCoupled) 1319nmLaser 633nmLaser LaserPower ControllerMonitor Shutter WeatherStati... Open at page → 24 Page 24 interferencedoesnotoccurinthem.Thinopticalelementsareavoided,becauseevenwhentilted,athin elementcanstillproduceinterferencefringes. Thelasersusedinthestabilizedsourcemustmeetseveralcriteria.Ideally,thelasersshouldproduce... Open at page → 25 Page 25 powertoabout2mWattheinputtotheLPCmodulator.Attenuator 1usesneutral-density reflective filters,andattenuator2usesabsorbingglassfilters;bothareplacedinthebeamatasmallangleto preventinterference. Lenses 1and2andthemountedpi... Open at page → 26 Page 26 theGaussianbeammodeldescribedinAppendixD.Thesizeofthebeamwaistformedbetweenthe lensesisalsodeterminedusingthemodel. Theopticalshutterusesaplastic-coatedbladethatopensandclosesquickly,withrisetimesanddelays thatarelesstha... Open at page → 27 Page 27 TheLPCmodulatorandLPCmonitorareeachhousedinidentical,precision-engineered enclosures.The beampassesthroughthedeviceswithnoappreciablehorizontaloffsetorangulardeflection,butasmall verticaloffsetisproduced.Theenclosureshav... Open at page → 28 Page 28 polarizationwithPolarizer2issimple.However,tominimizethepowerlossandmaximizethedynamic rangeofthesystem,thepolarizationangleofthelasersource.Polarizers 1and2,andtheLPC modulator'sinternalpolarizershouldallbesetascloseasp... Open at page → 29 Page 29 uncertaintywasassessedfortheexpectedspilloverandthemonitorwasusedtodeterminewhetherthe actualamountofspilloverwaswithintheassesseduncertaintylimit.Thespilloverwaslatercorrected for,toobtainlowercalibrationuncertainties.... Open at page → 30 Page 30 highvacuuminsidetheradiometertoinsulatethecoldinteriorfromtheexternalenvironment,whichalso eliminatesanyconvectiveheatflowinsidethedevice,butnecessitatestheuseofawindowthatallowsthe lighttoenterthedevice. Laser-optimized... Open at page → 31 Page 31 Asperthemanufacturer'srecommendation, theLOCRisbroughtbacktoroomtemperatureweekly. Leakagesthroughtheo-ringsealsinthecryostat,valves,andwindowmounthavethepotentialfor creatingiceontheopticalreceiver,thuschanging itsoptic... Open at page → 32 Page 32 Thermalmodeling[11.12]showedthat whenoperatingatthenominalreceiver temperatureof5.4K,theinequivalence betweenelectricalandopticalheatingis negligible(0.0005%).evenwhenthe opticalheatingpowerisappliedatan extremelocationo... Open at page → 33 Page 33 receiver'stemperatureideallyneverchanges,themeasurementofopticalpowercanbeperformed relativelyquickly.Thetemperaturecontrollersalsohavean"open"modeofoperation,wherethey simplyapplyafixedamountofheatingpower.Openmodeisuse... Open at page → 34 Page 34 voltagedropsacrosstheresistors andV^^aremeasuredusingthecaUbrationsystem'sprecision multimeter.ThepowerdissipatedintheresistorR^^,calledP^,isgivenby: ^H=n-/-- (1) Thepower determinedusingthemeasuredvoltagesisthencompared... Open at page → 35 Page 35 receiverelectricalpowerusingthetemperature controller'sopenmode,allowingthereceiverto reachitssteady-statetemperature,andmeasuring theresultingtemperature.Then,thetemperature controller issettomaintainthemeasured tempera... Open at page → 36 Page 36 Thewindowmountisconnectedtoakinematicgimbalmount,thatallowspreciseangularadjustmentof thewindowalongverticalandhorizontalaxes.ThewindowmountgimbalalsoholdstheNW40 clampingvacuumflange.Theclampingflangeallowseasyremovalof... Open at page → 37 Page 37 'start)-^ Initializesystem Alignlasersource Adjustandmeasurebeamdiameter AlignLOCR Measure LOCRwindow transmission Measurerelative aperture transmission Align detectors Setpowerto desiredlevel Yes } r MaintainLOCR Measur... Open at page → 38 Page 38 4.CALIBRATIONPROCEDURE Operationofthehigh-accuracycahbrationsystemistoocomplextoexplainhereindetail,butcomplete operatingflowchartsforthehigh-accuracycalibrationsystemareavailableintheformofanunpublished documentcalledth... Open at page → 39 Page 39 Whencustomerssubmitadetectorforcalibration,theminimuminformationtheymustprovideisthe wavelengthandpowerlevelofthedesiredcalibration.However,theymayalsospecifythedesiredbeam size,wavefront,ordivergence.Forexample,theymayr... Open at page → 40 Page 40 Inthecalibrationreport,thebeamusedinthecalibration isdescribedinseveralways.Thebeamis describedbyits1/e^intensitydiameteranditsfull-widthdivergenceangle,inthedetectorplane,andby itsGaussianbeamwaistdiameterandlocationrel... Open at page → 41 Page 41 Currently,acommercialdeviceisusedtomeasurethecalibrationbeam'sintensityprofile.The commercialdeviceusesascanning-slitbeamdiametermeasurementtechnique [15|.Ihescanning-slit techniqueaccuratelymeasuresaGaussianbeam'sprofil... Open at page → 42 Page 42 Thebeam'sincidenceangleisadjustedrelative tothedetector'sphysicalentranceaperture.To determinethebeam'sincidencerelativetothe aperture,theoperatorholdsaglassflatupto theaperture,sothatastrongspecularback reflectionisprod... Open at page → 43 Page 43 Aconservativeuncertaintyestimateoftheerrorinthedetector'saHgnment isassessedandstatedinthe calibrationreport.Typicalupper-boundsare1mmforvisualcenteringusingaruler,0.5mmforvisual centeringusinganaperturecross-hairorother... Open at page → 44 Page 44 detectorisusedwithvisiblewavelengths,andtheGedetectorisusedwithnear-infraredwavelengths. Therelativetransmittanceofthefixedcircularaperturesismeasuredusingthestandarddetector.The detectorisangledslightlysothatitsbackrefl... Open at page → 45 Page 45 showninFigure6fullyenclosesacenteredcircularaperturewithadiameterof7.8mm.Sincecircular aperturesoffractionalsizesarenotused,thecircularapertureof7mmdiameteristhelargestthatisfully enclosedbythedetector'sapparentaperture.... Open at page → 46 Page 46 voltagesandvoltageerrorisprovided.Themeasuredvoltageerrorsarecorrectedinpost-processing, as describedinAppendixF. Thesoftwareusedtocontrolthecalibrationsystemwillrequiremaintenanceintheformofaddingnew featuresanddebuggin... Open at page → 47 Page 47 inadevicesimilartotheLOCRwasnotflat.Theoreticalanalysisbasedonthereflectioncharacteristics ofthepaintandthegeometryofthereceiverconcludedthatthespectralresponseshouldbeessentially flatfromvisibletonearinfraredwavelengths... Open at page → 48 Page 48 thegastothevent,whereappropriate.Theventilationfan'sspeediscontrolledfrominsidethelaboratory sothattheairexchangeratecanbeincreasedwhenneededandreducedwhennotneeded. TheHegascauseslessdisplacementofOj,becausethereisusual... Open at page → 49 Page 49 Theliquid-heliumreservoirissignificantlydifferentfromtheliquid-nitrogen reservoirandpresentsa greaterdanger.Theprimarydifference isthatthereisonlyonefillportontheliquid-heliumreservoirand itsportisvacuuminsulatedsoitisve... Open at page → 50 Page 50 Caremustalsobeexercisedwhenusingthevacuumsystem,ordamagecanresult.Forexample,ifa vacuumsealoravalveisopenedatthewrongtime,ainrushofaircanoccur,whichwouldlikelydestroy theLOCR'sfragileopticalreceiver.Also,thecleanlinessof... Open at page → 51 Page 51 liquid-nitrogentemperatureandtheliquidnitrogen'srateofboilingwillslow.Whenfullyprecooled,the liquidnitrogeninsidethewell-insulatedliquid-heliumreservoirwillpracticallystopboilingentirely. Thentheliquidnitrogencanbeblowno... Open at page → 52 Page 52 4.2.2Alignmentandspatialuniformitymeasurement :ThefirststepinaligningtheLOCRistocenterthe laserbeaminitsopticalreceiver.TheLOCRisfirstcoarselyalignedsothatatleastpartofthelaser beamenterstheopticalreceiver.TheLOCRalignme... Open at page → 53 Page 53 ^ DustCover /WindowMount Figure15.TheNISTBrewster'sanglewindowmount,showingtheverticaloffsetofthe incidentlaserbeam. strikestheopticalreceiver,theLOCR'sreceivermustberealignedaftertheanglesareadjusted,andthen thewindowBr... Open at page → 54 Page 54 LOCR'sopticalaxiswhenitsgimbalmountisusedtoeffectaroll.Thewindowmountdoesnothavea roll-angleadjustment; itsrollangleissetwhenthemountisboltedtogether.Toreducethisproblem,the slopeofthewindow,whenitsgimbalmount'sadjustmen... Open at page → 55 Page 55 time-consuming; instead"TCALVER.EXE" isusedtomeasuretheerroratonlythepowerlevelsthatare actuallyusedintheopticalcalibration.Whileusing"TCALVER.EXE" addscomplexitytothepost- processingintheformofanelectricalcalibrationcor... Open at page → 56 Page 56 placedoverthewindowmountandrotatedtoitskeyedposition.Astripofadhesivepaperisattachedto thefrontofthedustcover,thepreciselocationwherethelaserbeamstrikesthecoveristhenmarkedon thepaper.WhentheassemblyisremovedfromtheLOCRf... Open at page → 57 Page 57 significantly.Forexample,tomeasure 1mWofopticalpower,theelectricalreceiverpowermustdrop from2.0to1.0mW;achangeof50%.Similarly,whenarelativelysmallopticalpowerisapplied,the electricalpowerhastochangerelatively little.Fore... Open at page → 58 Page 58 Theperiodoverwhichdataaresampledafterstabilizingiscalledtheratingperiod.WiththeLOCR,a ratingperiodlongenoughfortheacquisitionof30samplesisusuallyused.SincetheACR.EXEprogram samplestheLOCRatarateofapproximatelyonceevery1.... Open at page → 59 Page 59 theamountofliquidremainingcanalsobeinferredbythecontainer'sweight.However,theHquid- heliumcontainerdoesnothavealevelsensor,soadevicecalledathistletubeisusuallyusedtomeasure theliquidlevel.Likethetransferline,thethistletu... Open at page → 60 Page 60 energybytheperiodoverwhichthepowerwasapplied.Inthehigh-accuracycalibrationsystem,the averagepowerismeasured.Theperiodoverwhichthepowerwasappliedisalsoaccuratelymeasured, forconversionfromaveragepowertototalenergy,andvise... Open at page → 61 Page 61 Thesinglebaselinemethodisusedwithsomemeters,typicallybecausetheyhavenegligibledrift, respondslowlyandsohavealongsettlingperiod,haveasymmetrical riseandfalltimes,ordonotreturn tothesamebaselineaftertheillumination.Thesing... Open at page → 62 Page 62 respectively.Thetestmeterwasilluminatedattimet^,where<t^<tj.Usinglinearinterpolation,the averagepoweratthetimeofthetestmeterillumination,calledP^,isgivenby P.=P.^{P^~P.)'f^ (6) ThepowersP,andPjaremeasuredattheLOCR'soptic... Open at page → 63 Page 63 ThespecificequationusedismodifiedasnecessarytogivethecaHbrationfactorintheunitsthatthe customerdesires.Inanycase,theequationusedisdefinedexplicitlyinthecalibrationreport. 53 Open at page → 64 Page 64 5.UNCERTAINTYANALYSIS Toachievehighaccuracy, itisdesirabletominimizeallthesourcesofuncertaintyasmuchaspossible. Buttokeeptheserviceaffordabletothecustomer,uncertaintymustalsobemeasuredinareasonable amountoftime.Soinsomec... Open at page → 65 Page 65 Table1.ExamplevaluesfortheLOCRprimarystandard'suncertaintycomponents. ComponentofUncertainty CorrectionFactor StandardUncertainty(%) WindowTransmittance(7^,"yw) 0.99962 0.0138 ReceiverAbsorptance(A^,m^^) 0.99987 0.0070 R... Open at page → 66 Page 66 heatinginequivalenceu^.ExampleLOCR-basedpowermeasurementuncertaintiesaregiveninTable1 andtheuncertaintycomponentsaredescribedbelow.ThecombinedstandarduncertaintyUp^ofthe LOCRprimarystandard'spowermeasurement isgivenby "p... Open at page → 67 Page 67 constantoverthegivenwavelengthrange,andmanylaboratoriesdoconsidertheabsorptancetobe constant.Butactualmeasurementofreceiverabsorptance,performedonareceiversimilartothe LOCR's,showthattheabsorptance isindeedwavelength-dep... Open at page → 68 Page 68 achievethesamereceivertemperaturewascompared.Themanufacturerperformedfivemeasurements; themeandisagreementbetweenthetwoheaterswas0.0017%,withastandarddeviationof0.002%. Thismanufacturer'smeasurement isconsistentwithvalue... Open at page → 69 Page 69 TheLOCR'sbackgroundpowerreadingsdriftwithroomtemperatureandotherenvironmental influences,asdiscussedinsection3.2.Thereforethedual-baselinemeasurementtechnique,discussedin section4.3.1,isusedwiththeLOCR;thetechniquecorrec... Open at page → 70 Page 70 5.2.3Uncertaintyoftheappliedenergy :Whenanenergymeteriscalibrated,theuncertaintyinthe appliedenergyisused.Theuncertaintyintheappliedenergyisthesameasthatfortheappliedpower exceptthattheuncertaintyu^Jofthemeasuredinjectio... Open at page → 71 Page 71 Table2.Exampleuncertaintiesfortheappliedpowerandcalibrationfactorcalculation. v.uiiipuiiciiLuiuiiLeridiniy CorrectionFactor oianuaiuunccridiiiiy y/o) winaow 1ransniiuance /^xw/ (j.vyyoz U.UljO ivccciver/\Dsorpiancc w^j^j... Open at page → 72 Page 72 uncertainty u^^jinthecorrectionfactor isgivenby (16)u KT V B Whenusingthesingle-baselinemethodfromeq(4),thecorrectionfactoranduncertaintyarethesameas withthedual-baselinemethod,becausethebaselineaveraginginthedual-baseli... Open at page → 73 Page 73 I -41.501 -41.5012- -41.5014- c y -41.5016 -41.5018- -41.502- 0.0 4.0 16.0 20.08.0 12.0 Time(s) Figure17.Theoutputcurrentfromanilluminatedphotodiode,showingtwodiscretequantization levels. asinglelevel,thentheassessedunce... Open at page → 74 Page 74 quantization inthebaselinewillbeinsignificantcomparedtothequantizationwhenthedetectoris illuminated,sothecombineduncertainty isessentiallythesameasthatfortheno-baselinemethod. 5.3.4Measurementrepeatabilityofthecalibratio... Open at page → 75 Page 75 Abetteralignmenttechniqueusesasmallapertureasanalignmentaid,suchasasmallholeinthecenter oftheaperturecover,ortheholethroughthecenterofanattachedopticalfiberadapter.Thebeamis centeredovertheholebyusingthedetectoritselftop... Open at page → 76 Page 76 modeliscombinedwithmeasuredparameterstoprovidevaluesforbeam'sdiameteranddivergenceat thedetector'sentranceaperture,andtheoreticalvaluesfortheGaussianbeamwaist'sdiameterand location. Sincesomeoftheseparametersaretheoretic... Open at page → 77 Page 77 Becauseofimperfections inthepolarizedlaserbeamandcomadistortioncausedbythetiltinthespatial filterlenses,thebeamproducedbytheopticalsourceisusuallyelliptical,withitslongaxisinthe horizontaldirection.Bothverticalandhorizon... Open at page → 78 Page 78 sourcebandwidth,Aisthevacuumwavelength,andCisthespeedoflightinvacuum,anupper-bound fortheone-halfpowerspectrallinewidthinvacuum(AA)isgivenby 2C AA=A7 r. (24) (2C+AAv)-(2C-AAv) ^ ^ Byobservingthewavelengthmeter's"trigger"... Open at page → 79 Page 79 temperaturecan.Thetemperaturedifferencebetweenthedetectorplaneandtheopticalsourceisusedto estimatethesizeofthetemperaturegradient inthevicinityofthedetectors.Theuncertaintyinthe weatherstation'smeasurements isdeterminedb... Open at page → 80 Page 80 REFERENCES Note.Brandandcompanynamesareusedhereonlysothatthesystemcanbeduplicated,andimply neitherendorsementbytheNationalInstituteofStandardsandTechnology(NIST),northatthematerials orproductsidentifiedarenecessarilytheb... Open at page → 81 Page 81 [16] J.M.Houston,andD.J.Livigni,"ComparisonoftwocryogenicradiometersatNIST,"Natl.Inst. Stand.Technol. J.Res.106(4):641(2001). [17] O.R.Touayar,J.M.Coutin,andJ.Bastie,"MeasurementofthereflectanceoftheENM cryogenicradiomet... Open at page → 82 Page 82 APPENDIXA.Glossary Someofthemoreunusualorpotentiallymisunderstoodtermsandabbreviationsusedthroughoutthis documentaredefined.Inthissection,termsthataredefinedhereareshowninitalics. ApparentAperture:Theapparentapertureisan... Open at page → 83 Page 83 resultsfromtherotations,becausewhenadetectorisaligned,therotationsareadjustedbeforethe translations.Howevertoaidinthevisualizationoftherotations,therotationalaxescanbeconsideredto passthroughthecenterofthedetector'smass,... Open at page → 84 Page 84 usessimpleprocessesthatcanbeaccuratelymodeled.CryogenicradiometersliketheLOCRare currentlythebestprimarystandardavailableforopticalpowermeasurement, intermsofabsolute accuracy. RelativeApertureTransmittance:Therelativeap... Open at page → 85 Page 85 butthedetectoraloneissometimescalibrated.Thetestdetectorcanbeanopticalmeterofeitherpower orenergy. TransferStandard:Alaboratorystandardthatmaynotbesuitableasaprimarystandard,butistraceable toaprimarystandardthroughcalibr... Open at page → 86 Page 86 APPENDIXB.InstructionsforSubmittingMetersforCalibration 1.SelectthecalibrationservicefromtheNISTCalibrationGroupCalibrationServicesUsersGuideSP 250AppendixFeeSchedule.Theguideisavailableinthefollowingways: A.Fromcalibrat... Open at page → 87 Page 87 informNISTiftheirdetectorcannotbecleanedinthisway,thenthecleaningstepwill beskippedfortheirdetector. E.Thedesireddetectororientation.Thesystemusesapolarizedbeam,sodetector orientationcanbesignificant. F.Thedesireddetecto... Open at page → 88 Page 88 APPENDIXC.SampleCalibrationReport Asamplecalibrationreportisshownonthefollowingpages.Thereportdetailsacalibrationwherethe customerprovidedthreephotodiode-based detectorsandoneammeter,whichwerecalibratedasaunit (eachdetec... Open at page → 89 Page 89 Nisr U.S.DEPARTMENTOFCOMMERCE NATIONALINSTITUTEOFSTANDARDSANDTECHNOLOGY ELECTRONICS&ELECTRICALENGINEERINGLABORATORY Boulder,Colorado80305 ReportofCalibration for LASERPOWERMETER [Manufacturername]Model:[model#],SerialNo:... Open at page → 90 Page 90 LASERPOWERMETER Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] [Manufacturername]Picoammeter,Model[###],S... Open at page → 91 Page 91 LASERPOWERMETER Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] [Manufacturername]Picoammeter,Model[###],S... Open at page → 92 Page 92 LASERPOWERMETER Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] [Manufacturername]Picoammeter,Model[###],S... Open at page → 93 Page 93 LASERPOWERMETER Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] [Manufacturername]Picoammeter,Model[###],S... Open at page → 94 Page 94 LASERPOWERMETER Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] [Manufacturername]Picoammeter,Model[###],S... Open at page → 95 Page 95 LASERPOWERMETER Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] Model:[Manufacturer,Model#],SerialNo:1,NISTID:[#####] [Manufacturername]Picoammeter,Model[###],S... Open at page → 96 Page 96 APPENDIXD.GaussianBeamModelandSpatialFilterPinholeSelection TheopticalelementsconsideredintheGaussianbeammodelareshowninFigureD.l.Elementsthatdo notaffecttheshapeofthebeamdeliveredtothedetectorplane,suchasthebeamsteering... Open at page → 97 Page 97 TheresultingmagnificationofthecollimatedbeamisgivenbyM=DJD- f^lfyThediameterofthe beamoutputbythetwolensesofthespatialfiltercanthereforebeadjustedbyselectingtheratioofthe focallengthsofthelenses.Thisequationcanbeusedtose... Open at page → 98 Page 98 matrixestogether.Thebeamtravelsdownthez-axis,whichiszeroattheinputtothelensinthelast region.Thetransformmatrixisaccurateforz>0(intheregionatandpastthelens);thematrixforthe previousregionisusedtopredictthebehaviorbeforeth... Open at page → 99 Page 99 f, 0^ ' 1- +2 V fmJ ^Om \ f 0' 2 f \ V JmJ ( ' "1 1 + ('-f)l (D-4) Theradiusofcurvatureofthewavefront(R^iz))atadistanceofzfromlensmisgivenby 1- .+2 V JmJ ^Om ^ JmJ. 2 1 2 V /myJ ^ 1 /fm \ JmJ (D-5) Theimagewaistoccurrsad... Open at page → 100 Page 100 SeveralinterestingresultsareobtainedfromtheGaussianbeamanalysis,perhapsthemostsignificantof whichishowaGaussianbeamiscollimated.Ageometricallycollimatedbeamisusuallythoughtofas havinganinfiniteradiusofcurvature,orplanarw... Open at page → 101 Page 101 distancebetweenthelaser'soutputandLens 1)and^2(thedistancefromLens2tothedetectorplane). Thedistanced^isdifferentforeachlaser,butdyisconsideredtobeconstanteventhough itchanges slightlywhenLens2'spositionisadjusted,because... Open at page → 102 Page 102 ofthelens,soIj=V2=/2-Inthedetectorplane,thebeamsize(w^p)andradiusofcurvature{R^^)aregiven byeq(D-10)andeq(D-11)withm=2andz=dj.However,thesystemisseldomusedwiththeoutput beamoptimallycoUimated;inpracticethedetectorplanebe... Open at page → 103 Page 103 P=H QQ I 1 I I I I I I I I I I I I I I I I I L -10.0 -5.0 0.0 5.0 10.0 Lens2Displacement(mm) FigureD.3Theradiusofcurvatureofthewavefrontinthedetectorplaneversusthe displacementofLens2fromtheoptimallycollimatedlocation. l... Open at page → 104 Page 104 -10.0 -5.0 0.0 5.0 10.0 Lens2Displacement(mm) FigureD,4ThedistancefromLens2totheprojectedwaistimage{I2)versusthedisplacement ofLens2fromtheoptimallycollimatedlocation. TheabsolutevalueoftheradiusofcurvatureisshowninFigur... Open at page → 105 Page 105 similartothatshowninFigureD.2,exceptthatthebeamradiusvariesfrom0.35to3.5mm.As6is increasedfromzero,thefirsttimethewaistcrossesthedetectorplaneithasadiameterofapproximately3 mm.As6isincreasedfarther,thesecondtimethewaistc... Open at page → 106 Page 106 Thefull-widthbeamdivergenceangleinthedetectorplane(0^^)canbederivedfromtheradiusof curvatureinthedetectorplane(R^p),givenbyeq(D-5)withm=2,=/2+6,andz= Theequation relating0^^toR^^isgivenbythefollowing;theapproximation isa... Open at page → 107 Page 107 whichcomplicatestheselectionofthepinholesize.Inthehigh-accuracycalibrationsystem,arelatively largepinholeisusedtominimizethedegradationofthelaserbeam,alreadyonlyapproximatelyGaussian. Thecalibrationsystem'sspatialfilterc... Open at page → 108 Page 108 Inpractice,thespatialfilterpinholeisselectedfromasmallnumberofavailablepinholesizes,with diameterstypicallyspaced10to100^imapart.Selectingtoolargeapinholeisbetterthanselectingtoo smallapinhole,sincewearemoreconcernedwith... Open at page → 109 Page 109 APPENDIXE.RelativeApertureTransmittance:EstimationandUncertainty AGaussianlaserbeamcanresultinpowermeterswithdifferentsizedorshapedlimitingaperturesto absorbdifferentamountsofpower,becauseofthedifferenceintheiraperture's... Open at page → 110 Page 110 apertureestimatesanequivalentlimitingaperture.Withthesedetectors,theapparentaperturemaynotbe exactlyequivalenttoalimitingaperture,becausewithatruelimitingaperture,thedetectorhasno responsetolightoutsidetheboundarydefined... Open at page → 111 Page 111 c<3 1-1 <: > eg 1.0 0.8 - 0.6 - B 0.4 0.2 i.O 4.0 633nm 1319nm 1550nm Gaussian 5.02.0 3.0 ApertureDiameter(mm) FigureE.lMeasuredandtheoreticalrelativeaperturetransmittanceforsmallcircular apertures,relativetoacircularref... Open at page → 112 Page 112 practiceasmallerbeamwouldprobablybeusedwithsuchsmalldetectors,butthefigureclearlyshows thesignificantdifferencebetweenthemeasuredandtrueGaussianbeamtransmittance. FigureE.2shows therelativeaperturetransmittanceformorepra... Open at page → 113 Page 113 Themeasuredrelativeaperturetransmittanceforthreeadditionalwavelengths(488nm,515nm,and 633nm#2)areshowninFigureE.2;theywereacquiredmorerecentlythantheothers,andbetterreflect thecurrentuncertainty inthemeasurement.Theother... Open at page → 114 Page 114 translatingtheexternalcircularapertureinfrontofthetransmittancemeasurementdetector,and measuringthechangeintheresponseofthestationarydetector.Anupperboundisplacedontheaperture misalignment;a0.5mmboundiscurrentlyused.Thed... Open at page → 115 Page 115 backgroundaroundthebeamisnecessary.Whenasingle-elementdetectorortrapwithabackreflection isused,itisplacedinthebeamatasmallangletopreventtheback-reflectionfrominterferingwiththe incidentbeam.Currently,aSitrapdetectorwitha... Open at page → 116 Page 116 ThemeasurementsofthepowersP,,P-,,and containuncertaintiesduetotheimperfectcenteringofthe aperturesaroundthelaserbeam.Thecenteringuncertainty isestimatedinaseparateexperiment, describedbelow,whichprovidesanestimateofthest... Open at page → 117 Page 117 Becausetheactualcenteringuncertainty isassumedtobelessthanthe±0.5nuntranslationusedinthe measurement,thequantitiesPQiR_^{d)- 1)andPq(R(d)- 1)estimatetheboundsofthechangein transmittedpowerduetocenteringuncertainty.Arecta... Open at page → 118 Page 118 detector'saperturerelativetothestandard'saperture,thetransmittanceofthestandard'saperturerelative tothereferenceapertureisdetermined.FortheLOCR'sellipticalaperture,method2isused. 1.Estimationoftherelativetransmittancefor... Open at page → 119 Page 119 u,,{D,C) ul,{D,,C)+ul,{D„C)+ {t,,{D,,C)-T,JD,,C)) (E-14) 2 3 Thetransmittanceofthedetector'saperturerelativetothestandard'saperturecanthenbecalculated usingeq(E-11),withuncertaintycalculatedusingeq(E-12). 3.Estimationoft... Open at page → 120 Page 120 Thecombinedstandarduncertaintyu^^iD,S)isgivenby M„,(D,5) RA T,AS,C. uIai,C)+ r,(D,/)r,(/,c) , iil,{S,C). (E-16) Whenthedetector'sapparentapertureislargerthanthereferenceaperture,thereferenceapertureitself canbeusedasthei... Open at page → 121 Page 121 APPENDIXF.SystemDMMandLOCKElectronics:CalibrationandCorrection Alloftheelectricalsystemsthataredirectlyinvolvedinthedetectorcalibrationaretraceabletothehigh- accuracycalibrationsystem'sdigitalmultimeter(DMM),whichistrace... Open at page → 122 Page 122 uncertaintyspecificationsincludethedevice'stemperaturecoefficientforarangeof±5°Caboutthe calibrationtemperature.Thelaboratorytemperature isnormallywithinthisrange,soaddingadditional uncertainty isnotusuallyneeded. Ifthet... Open at page → 123 Page 123 TableF.2DMMresistancecalibrationvaluesforthefrontinputterminalsandforthe1000Q range. Indicated Resistance Resistance Offset /?c (mQ) StandardUncertainty /?r(Q) Uf^Q(mQ) Mrs(mQ) (mQ) Wr(%) 1000 -174.8 4.3 2.7 5.0 0.00050... Open at page → 124 Page 124 TheLOCRheater'sresistance iswithin 1%ofthestandardresistor'sresistance;sotosimplifythe followinguncertaintyanalysis,theyareconsideredequal.ThusR^^=R^-R, =Vj=V,andtheapplied electricalpowercanbesimplifiedto Theamountofabs... Open at page → 125 Page 125 Thecovarianceterminthelawofpropagationofuncertainty isestimatedbym(V,,V^)= Wvi"v2'where thetermk^^istheestimatedvoltagecorrelation.Theothercovariancetermsarezerosincethe uncertaintyinRisuncorrelated. Inthelimitingcasewhe... Open at page → 126 Page 126 timestoassesstherandomcomponentoftheuncertainty,buttheuncertaintyintheelectrical measurementsthemselves isaccountedforelsewhere,inA;,,sotheindicatedelectricalpowersareassumed tobeaccuratehere. WhentheLOCRisusedtomeasurea... Open at page → 127 Page 127 table,asinglemeasurement ateachindicatedpowerisshown,butinpracticethemeasurementsshouldbe performedmultipletimes.Forsimplicity,suchmultiplemeasurementsarenotpre-averaged;butifit becomesdesirabletoreducethisuncertainty,pr... Open at page → 128 Page 128 ThecorrectionfactorkjanditsuncertaintyaregiveninTableF.5usingthedatafromTableF.4.The valuesforanominalpowerof1.99mW,usedinthe0.01mWcalculations,areinterpolatedfromthe resultsforpowersof1.9and2.0mW.Threeuncertaintyestimat... Open at page → 129 Page 129 APPENDIXG.LOCKOpticalReceiverAlignment:Uncertainty Itisusuallyassumedthatwithcryogenicradiometers,theopticalreceiver'sabsorptance isuniformwithin itsapparentaperture.However,arecentpublication [8]suggeststhatdifficulties... Open at page → 130 Page 130 withintheentirecircularregion.Averticaltranslationofthebeam'slocationinthereceivercannotbe performed.Totranslatethebeamvertically,theentireopticalsourcebreadboardmustberaisedor lowered.Currently,thisinvolvesmanuallyadjus... Open at page → 131 Page 131 aperturetransmittancevaluesarecalledT^(x),withstandarduncertainty Ujf^{x).Liketheresponsivity measurements, thetransmittances arealsomeasuredrelativetothetransmittance atthenominalcenter,so eachmeasurementhasavalueof1ata... Open at page → 132 Page 132 TableG.lExampleLOCRalignmentuncertaintydata. X=~ .1.0mm X—0.5mm A=0* X=0.5mm X= 1.0mrn Value 'sfrl 1Inr OLU.UUL. ValLie Sfd IInr V3.1uC <^tfl IInr V3.IuC sfH IInrOIU.UIiC k=633nm R(-x) U.UUUU2U u.y9yyu2 U.UUUUZJ 1AAAAAA... Open at page → 133 Page 133 APPENDIXH.WindowTransmittance:EstimationandUncertainty ThetransmittanceoftheBrewster'sanglewindowistheratiooftheamountofopticalpowerthatis incidentonthecryogenicradiometer'sopticalreceiverwhentheradiometer'swindowisinpla... Open at page → 134 Page 134 Otherpotentialsourcesofuncertaintyareinsignificantcomparedtothesefactors,soarenotincludedin theuncertaintyanalysis.Twosuchinsignificantuncertainties are:imperfection inthescatteredoptical powermeasurement,andthechangeint... Open at page → 135 Page 135 Thepresenceofthewedgeandthevacuumonthebackofthewindowalsocausethedirectionofthe transmittedbeamtodeviateslightlyfromthedirectionoftheincidentbeam.Fortheperfectlyparallel window,thevacuumonthebackofthewindowcausesthetrans... Open at page → 136 Page 136 nominalbeamlocationinthesecondsetofmeasurements,becauseofimperfections inthemounting hardware.Therefore,thetransmittancevalueatalocationix,y)inthetwomatricesmaynotrepresentthe samephysicallocationonthewindow.Thelocations... Open at page → 137 Page 137 Theuncertaintyin7"^^^,containscontributionsfromboththemeasuredvariationandtheuncertaintymthe measurement.Thestandarddeviationoftheninesamplesisusedasthestandarduncertainty thatisduetovariationinthetransmittance. (H-6) 1=... Open at page → 138 Page 138 H.3ExampleCalculationofTransmittance Thefollowingexampleusesactualwindowtransmittancemeasurementdataacquiredwitha633nm wavelengthlaser.TableH.lshowswindowtransmittancedataacquiredbeforethecalibrationswere performed(initi... Open at page → 139 Page 139 APPENDIX I.Center-WeightedSpatialUncertainty Dr.Chih-MingWang,NIST,StatisticalEngineeringDivision Assumethatthetransmittance at(x,y), t{x,y),canbemodeledapproximatelybyasmoothcurve,saya quadraticform,withinagivenwindow;t... Open at page → 140 Page 140 '0.9994575' / 1 - 1 1 1.17174 - 11.17174' 0.9994220 1- 1 0 1.17174 0 0.17174 0.9992600 1- 1-11.17174 1 1.17174 0.9993700 1 0 1 1.17174 0 1.17174 0.9993225,x= 1 0 0 1.17174 0 0.17174 0.9993585 1 0-11.17174 0 1.17174 0.999... Open at page → 141 Page 141 Wecanalsoevaluatetheuncertaintyinestimatingspatialtransmissionduetoerrorsinlocating(x^Jo)- Thevariance,assumingindependenceofXqand y^,, isgivenby Asmallexperimentcanbeconductedtoestimatevar(xo), var(>'o^). 131 Open at page → 142 Page 142 APPENDIXJ.EstimateofLOCKOpticalReceiverAbsorptance TheabsorptanceoftheLOCR'sopticalreceiverwasmeasuredatawavelengthof633nmbythedevice's manufacturer [13].Thereceiver'sabsorptance atotherwavelengths isestimatedusingmeasur... Open at page → 143 Page 143 TableJ.2Receiverabsorptanceuncertaintycalculation. ReceiverAbsoq)tance at633nm (^R633) TypeAUncertainty Estimate ('<ta) TypeBUncertainty Estimate ("tb) CombinedStandard Uncertainty 0.999919 0.000002 0.000002 0.000003 dev... Open at page → 144 Page 144 showthattheabsorptanceshouldvarysmoothlythroughoutthewavelengthregion,withnoresonance peaksordips;thereforetheassumptionthatthemeasurementsareavalidstatisticalsamplingofthe absorptanceshouldbevalid.Thisanalysisisconsider... Open at page → 145 Page 145 TableJ.3LOCRreceiverabsorptanceatwavelengthsotherthan633nm. Wavelength Reflectance Absorptance (nm) A{X) uJX) 325 0.000123 0.000016 0.999877 0.000016 488 0.000231 0.000030 0.999769 0.000030 515 0.000177 0.000019 0.999823... Open at page → 146 Page 146 APPENDIXK.WeatherStationCalibrationandUncertainty Environmentalparametersaremeasuredusingacommercialweatherstation[35].Toobtainaccurate measurementswiththeweatherstation,itstemperatureandbarometricpressurefunctionsarecal... Open at page → 147 Page 147 usingaTypeAanalysisofthesensorcalibrationdata.Foreachsensormeasurement,thedifference betweenthestandard'stemperatureandthestation'sindicatedtemperature isgivenbytheamountdj. Thecorrectionfactorforthesensor,k^,isthentheme... Open at page → 148 Page 148 (73 S CD 25.32 25.28 - 25.24 X25.20 - 0 10 4020 30 Time(min) FigureK.lInternalweatherstationtemperatureduringatypicalopticalcalibration. 50 O25.1 <^ 225.0 u S <u ^ 24.9 cd -24.8 0 10 4020 30 Time(min) FigureK.2Externalwe... Open at page → 149 Page 149 TableK.2Calculatedtemperaturesanduncertaintiesfortheexampledata. InternalTemperature (°C) ExternalTemperature ("C) Calibrationfactorsk^, -0.144 -0.071 Calibrationfactorstandarduncertainty i/^,h^^ 0.063 0.060 iVlt/alllllU... Open at page → 150 Page 150 ThetwoNCARlaboratoriesarelocatedwithinafewmilesofthehigh-accuracycalibrationsystem,at altitudesaboveandbelowthesystem. ThepressureatthecalibrationsystemisinterpolatedfromthepressureatthetwonearbyNCAR laboratories.Theinte... Open at page → 151 Page 151 dA ws wsJ ws dA FJ dp, ws dA (dp. MJ WS dP dP. WS MJ dP, •PF (K-4) FJ Toevaluateu^,theuncertaintyofthestatedaltitudesandNCARpressurereadingsareneeded.We assumeastandarduncertaintyfortheNCARaltitudesof2m,som^^,= =2m.Weuse... Open at page → 152 Page 152 Thenominalpressureduringthecalibration,calledP,isthesumofthemeanindicatedpressure,P\^\,and thepressurecalibrationfactor,k^.Thecombinedstandarduncertainty inP,calledMp,isthequadrature sumoftheindependentuncertaintiesu^,u^... Open at page → 153 Page 153 specification isinvalid,becausethepublishedspecificationsforthetemperatureandpressuresensors seemconservativewhencomparedtotheactualperformanceofthesensors.Theaccuracyspecification forboththeinternalandexternaltemperatur... Open at page → 154 Page 154 TableK.6Calculatedrelativehumidityanduncertaintyfortheexampledata. RelativeHumidity(%) Meanrelativehumidity,RH 31.08 Measuredrelativehumidityvariation,m^m 0.27 Standarduncertaintyofthesensorcalibration,w^s 5.00 Outputqua... Open at page → 155 Page 155 TechnicalPublications Periodical JournalofResearchoftheNationalInstituteofStandardsandTechnology—ReportsNISTresearch anddevelopment inthosedisciplinesofthephysicalandengineeringsciencesinwhichtheInstitute is active.These... Open at page → 156 Page 156 U.S.DepartmentofCommerce NationalInstituteofStandardsandTechnology 325Broadway Boulder,Colorado80305-3337 OfficialBusiness PenaltyforPrivateUse,$300 Open at page →