FROG Q and A of FROG 2012-02-07

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1、QuestionsandAnswersofFROG1.Q:WhatisthedifferentofAutocorrelationsandFROGwhenmeasureultra-shortpulse?A:Autocorrelationsalwayssmearoutstructureofpulsesandweshouldassumethepulseshapebeforewemeasureit.IngeneralweassumethatitisaGaussianpulseshape.ACcouldberightwhenthepul

2、sehasnostructureandithasaGaussianshape.Butifthepulsehassomestructure,youcouldn’tassumethatitisaGaussianandtheresultisnotreliable.Forexample:Anautocorrelationtypicallycorrespondstomorethanoneintensity.Thustheautocorrelationdoesnotuniquelydeterminetheintensity.Evennic

3、eautocorrelationshaveambiguities.ThesecomplexintensitieshavenearlyGaussianautocorrelations.Conclusionsdrawnfromanautocorrelationareunreliable.However,FROGcanmeasurepulseswithoutanyassumptionandcangivetheuniqueintensityandphaseofthepulses.Ingeneral,theSHGFROGhasatriv

4、ialambiguity,itisveryeasytofindoutandremoveit.Inprinciple,FROGmeasuresanykindofpulseswithoutanyassumptionbutthespectralresolutionandthetemporalresolutionlimittheaccuracyofmeasuringpulses.Forexample,ifthepulseisverycomplicate,itrequireshighspectralandtemporalresoluti

5、on.2.Q:Howtosetcalibrationnumbers?A:Acalibrationsheetissupposedtocomewiththedevice. MakesurethatthenumbersarethesamewiththenumberintheQF.7.Click“Configuration→CameraCalibrations”,makesurethatthevalueof“Delayincrement”and“Wavelengthincrement”arethesamewiththevalue“dτ

6、=2.36597”and“dλ=0.104601”whichshowinthebottomleftofcalibrationsheet.(ThistwonumbersarejustexamplesforSJTU’sFROG)1.Q:Howtosetthecamerarotation?A:Thecamerarotationshouldbe90degreeforthemodel15-40. Ifyougoto"configuration"and"cameracalibration"inQFmenu,youcanseeCamerar

7、otation.Ifitisnot90degree,youshouldmakeit90degree.2.Q:Whythecamerarotationmustbesetto90degree?A:Thereasonofusing90degreerotationisthatthetypicalspectrumof~40pulsesisverybroadandwearetryingtouselongerpartofthecamerachip.Ingeneralwhenacameraisupright,thehorizontalsize

8、ofthecamerachipislongerthantheother.3.Q:Polarizationofthebeam?A:Thedeviceusesasecondharmoniccrystalandsothepolarizationofthepulseisveryimp