PicoQuant MultiHarp 150 - Problems, Tips & Tricks; Basic Pitfalls; PC Performance Issues; Histogram Artefacts

PicoQuantGmbH MultiHarpSoftwareV.3.1.0.0
7. Problems, Tips & Tricks
7.1. Basic Pitfalls
ThehardwaresettingsintheMultiHarpsoftwareareretrievedtothecurrentsettingsuponloadinganexisting
measurementfile.Thisisaconvenientfeaturemostuserslikebecauseiteasilypermitsrepeatingameasure-
mentwithidenticalsettings.However,theretrievedsettingsmaybecomepitfallswhentheyarenotinagree-
mentwiththemeasurementyouareintendingtorun.Thismaybegeneralsettings(seesection6.7)aswellas
controlpanelsettings(seesection6.4).Ifmeasurementsbehavestrangely,alwayscheckyouractivesettingsin
bothplaces.
7.2. PC Performance Issues
TheMultiHarpdeviceanditssoftwareinterfaceareacomplexreal–timemeasurementsystemrequiringappro-
priateperformancebothfromthehostPCandtheoperatingsystem.ThisiswhyafairlymodernCPUandsuffi-
cientmemoryarerequired,alongwitharecentUSB3.x(orcompatible)hostcontroller.Thescreenresolution
shouldbeatleast800x600.Atleasta2GHzdualcore(betterquadcore)processor,4GBofmemoryandafast
harddisk(preferablySSD)arerecommended.
Inordertomaintaincorrectinteractionbetweenthemeasurementhardware,thedisplayofhistogramcurves
anduserinput,theoperatingsystem’smessagepassingmechanismisused.Itisrecommendednottooverload
thesystembyrunningotherprocessesinthebackgroundwhilemeasuringwiththeMultiHarp.ThePC’sown
occasionalnetworkactivityshouldbenoproblembutrunningthemachinee.g.,asaserverforotherPCsisnot
recommended.Inprincipleanykindofbackgroundactivityisallowed.However,shouldthesystembecome
overloaded,photoneventsmaybelostandmeasurementtimesanddisplayratesmaybecomeirregular.
YoucanminimizetherunningMultiHarpsoftwareduringmeasurementswithoutissues.Thismaybeofinterest
forlengthymeasurementsinintegrationmode,whereoneisonlyinterestedinaccumulatingacertainamountof
countswithoutneedforpermanentmonitoring.However,thethingsyoudointhemeantimemustnotoverload
theCPU.
The"panelmeters"showingthecurrentcountratesarenotmeanttobe100%accurate.Theymerelyserveas
anaidforsettingupthesystem.Someofthemmaysufferfromsystemoverload.Accordinglythevaluesshown
inthecurvedetails(tracemappingdialog)aresubjecttosuchtolerances.
InTTTRmode,systemoverloadwillmanifestitselfinlossofdataandterminationofthemeasurement.Espe-
ciallythereal-timecorrelatorrequiressignificantresources.Herenootherheavyloadbackgroundprocesses
shouldbeallowedtorun.ThefasterthePC,thelesstheseissueswillmatter.TTTRmodeperformance(i.e.
max.timetaggingthroughputtodisk)mayalsobeimprovedbyusingmodernsolidstatedisks.
7.3. Histogram Artefacts
Disturbinghistogramrippleisstronglydependentonthequalityoftheinputsignals.Trytodeliverthebestpossi-
blesignalqualitywithcleanandreasonablysteepactiveedgesandwithouttoomuchringing.Itisrecom-
mendedtousedetectorandsyncsignalsofsimilaramplitudetominimizecross-talk.Ifapicosecondpulsed
laserfromPicoQuant'sPDLSeriesisused,attenuatingthesyncpulsesby10dBimmediatelyatthelaserdriver
mayreducehistogramripple(settriggerlevelaccordingly).Alwaysusegoodquality50Ωcomponentsandcoax
leadswithpropershieldingandcorrecttermination.WerecommendcablesoftypeRG223withdoublebraided
andsilverplatedscreen.Checkyoursetupforgroundloops.Groundingdifferentsystemcomponents(PC,de-
tector,detectorpowersupply,diodelaserdriver,etc.)atdifferentpointscaninduceconsiderablenoiseinthe
groundlines.Becausesignalreturnpathsmaysharethesamegroundlines,thisnoiseiscopiedintothesignal
linesandcausesincreasedtimingjitterand/orhistogramripple.Networkcablesandmobilephonesmayalso
besourcesofnoise.Useproperlyimpedancematchedpowersplitters(reflection–freeT–pads)ifsignalsmust
befedtomultiple50Ωinputs.NeveruseordinaryBNCtees.AllaccessoriesareavailablefromPicoQuant.PMT
detectorsshouldbeconnectedthroughasuitablehighspeedpreamplifier(availablefromPicoQuant).MCP–
PMTdetectorsshouldbeconnectedthroughanamplifierwithslightlyhighergain(alsoavailablefromPico-
Quant).TTL–SPAD–detectors(e.g.Perkin–ElmerSPCM–AQRandsuccessorsbyExcelitas)mustbeconnected
throughanattenuatororattenuatingpulseinverter(e.g.,PicoQuantSIA400).
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