第十二讲 啁啾脉冲放大器

.,12.ChirpedPulseAmplication(CPA)andPetawattLasers,Chirpedpulseamplication(CPA)PulsestretchingmethodPulsecompressionRegenerateamplificationMultipleamplificationGainnarrowingOpticalparametricCPAPetawattlaserexamplePulsecontrast,.,Laserintensityevolution,引自G.MourouICUIL2008,CPALasers,.,ChirpedpulseamplificationScheme,.,CPA:Why?,EfficientamplificationAvoidopticaldamageinamplificationmediumduetohighopticalintensityReducethenonlineareffectinmedium,.,Pulsestretchingbygratingpair,.,PulsetobestrecthedduetoGDD,30fs+109fs23.08ns,.,Diffraction-gratingpulsecompressor,Thegratingpulsecompressoralsohasnegativesecond-orderphase.,Lsep,w,w,whered=gratingspacing(sameforbothgratings),Grating#1,Grating#2,Notethat,asintheprismpulsecompressor,thelargerLsep,thelargerthenegativeGDD.,.,Modelockedoscillatorasseedinglight,.,Regenerateamplifier,四分之一波电压放大器,.,Regenerateamplifier,半波电压再生放大器,.,OpticalIsolator,Function:(1)avoidtheamplifedlightfeedingbacktooscillator(2)Splitseedingandamplifiedbeam,.,Multi-passamplifier(1),.,Poweramplifier,.,.,Gainnarrowing,.,Suppressionofgainnarrowing,.,.,OPCPA,Nonlinearcrystal,Pumpinglaser:527nm,Seedinglaser:910or1053nm,OPCPAcharacteristics:(1)highgain(1000forsinglepass)(2)largeamplifyingbandwidth,wavelengthdesignable(3)Lowenergyconversionefficiency(4)requiressynchronizationbetweenpumpingandseedinglaser,.,Couplingwaveequation,.,Group-velocitymismatchlimitsbandwidth.,Takethesecond-harmonicpulsetohaveaGaussianintensity,forwhicht=0.44.Rewritingintermsofthewavelength,t=td/d1=0.44d/d1=0.442/c0whereweveneglectedtheminussignsincewerecomputingthebandwidth,whichisinherentlypositive.Sothebandwidthis:,CalculatingthebandwidthbyconsideringtheGVMyieldsthesameresultasthephase-matchingbandwidth!,.,560TWOPCPAbyRussia,.,MainRoutesforPetawattlaser,CPAbasedonTi:Sapphire:800nmwavelength;broadbandwidth(30fs),repetitive(0.1Hz);30JCPAbasedonNd:glass:1053nm,400fs,200J,oneshotperhours;OPCPAbasedonKD*P:40-80fs;910nmor1053nm,35J;singleshot,.,Petawattexample:petawatthybridOPCPA-Glasslaser-Texas,.,Petawattscheme,.,OPCPAscheme,.,Nd:glasshybridamplifier,.,Suppressiongainnarrowingbyhybridamplification,.,Compressiongrating,.,Results,.,Petawattlaserfacilities,.,Petawattlaserfacilitiesintheworld,.,PulseContrast:intensityofmainpulse/intensityofnoisepulse,引自AnnualReport2007LLE,Rochester,Definitionofpre-pulsecontrast,.,Thepulsecontrastcanbereducedsignificantlyduringitsgeneration,propagationandamplifications.Amongalltheprocesses,contrastdegradationduetoASEisfundamental(alwaysaccompaniedwithlaseramplification),引自AmplitudeDataSheet,.,ThenoisepedestalwillbemorecomplicatedinOPCPA.Temporalripplesinpumppulsewillalsodegradethecontrastsignificantly.,引自V.BagnoudOE2007,PumpnoiseOPG,.,DoubleCPAdesigntoboostcontrast,Nonlinearpolarizationrotation,Jullien,OL2004,CPAStage1,CPAStage2,NonlinearPulseCleaning,.,SHGboostcontrast,.,Question