第3讲飞秒激光技术及其应用

Ti:SapphireTi:SapphireTi:S1fs).NI(t)∝E02Sin2(Nωt/2)/Sin2(ωt/2)N2E02(ωt/2=mπ)T=2π/ω=2L/cτ=2π/Nω=2L/Nc=T/NN=ΔνG/ΔνΔνGΔν=c/2Lτ=1/ΔνGTi:Sapphire600—1150nmΔνG——τ——NtR6GΔλ50nmDn´t=0.3140.4410.886Ti:SLasert=3t5fs(4.5fs)(1999Guinnessrecord60Q-Switching10-9—10-10s(ns)70Modelocking10-11—10-12s(ps)Active,SynchronousPumping,PassiveModelocking80CollidingPulseModelocking10-13s(sub-ps)90KerrLensModelocking10-15s(fs)4.5fsT=2.7fs4.0fs8050nm1981R6GDODCI100fs198765fsOpt.Lett.12(1987)681198527fsOpt.Lett.10(1985)131100mW3-7WAr+90fsTi:Sapphire——1991D,E.Spenceetal,Opt.Lett.16,P.4260fs,845-950nm,300mW(6WAr+1997M.Nisolietal,Opt.Lett.22,P.52220fs4.5fs20μJ1KHzA.Baltuskaetal,Opt.Lett.22,P.10213fs5fs6μJ1MHz1999U.Morgneretal,Opt.Lett.24,P.4114.3fs(Sech),4.8fs(Gaussian)2T(2.7fs),200mW,90MHz,650-1050nmTi:S1KLM(KerrLensModelocking)----passive,simple,solidstatemodelockingn=n0+Δn(r),Δn(r)∝n2I(r)n=n0+Δn(r),Δn(r)∝n2I(r)n2∝ε0Re[χ(3)]χ(3)——NonlinearOpticsP=ε0χ(1)E+ε0χ(2):EE+ε0χ(3):EEELinearopticsNonlinearopticsReflectiondiffraction……nofrequencychangeEOeffectSHG,SFG,THGFour-wavemixingself-action(self-focusing,SPM)…...ELinearopticsNonlinearopticsωω0I0Iiω0ω0IiI0ω=2ω0,3ω0,…...Nochangeofω0PNL=ε0χ(2):EE+ε0χ(3):EEEχ(2)——χ(3)——Re—Im—n=n0+Δn(r),Δn(r)∝n2I(r)n=n0+Δn(r),Δn(r)∝n2I(r)n20,nLLrIrKLMn202SPM+GVDSPM(SelfPhaseModulation)Δn(t)∝n2I(t)Δϕ(t)∝I(t)dΔϕ(t)/dt=-Δωn20tΔωtdI(t)/dt0Δω0ωSPM(n20)Ti:S(n20)SPM(GroupVelocityDispersion)SPM+GVDn2,d2n/dλ20GVDn(λ)λdn(λ)/dλλ1λ2λ3Vg---Vg=c/n(1+λ/ndn/dλ)d2n/dλ20dVg/dλ0Chirpdn/dλ0+GVDGVDSPMGVDd2n/dλ2d2P/dλ20n20GVD----------1(BP1)2(BP2)4(Opt.Lett.Vol.9,1984,P.156)d2P/dλ2=4l{[d2n/dλ2+(2n-1/n3)(dn/dλ)2]sinβ-2(dn/dλ)2cosβ}P----620nmn=1.457,dn/dλ=-0.03059μm-1d2n/dλ2=0.1267μm-2d2P/dλ2=1.0354-l(7.4810-3)l138.4mmd2P/dλ20lβ——CPA1969E.B.TreacyIEEEJ.Quan.Electron.QE-5,454-458——δλτ=b(λ/d)dλ/{cd[1-(λ/d-sinγ)]}b---d---γ---λ=1064nm,γ=600,λ1-λ2=10nmδλτ(ps)=0.58d(cm)d=100cm,δλτ=58psstretcherAmplifierCompressorCPA:ChirpedPulseAmplifierttseedM1A1A2M2M3M4M5(6)_A3M8M9(10)M11L1L2L3P1M13M14M15M16M17M7M18M19(20)M21(22)_Mp1Mp2L4L5A6A5PC1PC2λ/4M12Ti:PumpStretcherCompressorOutputKHzNd:YAGlaser(Q-switched)0.6JSHG532nm/5nsSeedsource1nJ/840nm10.5fsstretchedto0.5nsBBOpre-amplBBO1mJ~0.6J15mJ840nm1000×15000×(OPCPA)OPCPA12ω0=800nm,2ω0,……11ω0,11250as1fs)Ti:SandCr:forsteritelasersarecoupledinsideTi:ScrystalbyM1,M2,M3,M4,F.C1,F.C2frequencycountersCr:Flaser(1250nm)T2outputcouplerTi:Slaser(820nm)T1outputcouplerZ.Wei,Opt.Lett.(2002)PulsetracesofTi:S(top)andCr:F(bottom)lasers(a)free-running(b)synchronization(a)Ti:Slaserτ=43±2fs(b)Cr:Flaserτ=52±1fsautocorrelationtwolaserscross-correlationτ=74±2fstimejitteronlyfewfemtoseconds)Phase-coherentopticalpulsesynthesistwoseparatefslasers(100MHz)760nm,810nmwavelengthsScience293(2001)1286————BoxcarL1GasjetGratingReflectorSlit3Slit2PMT1PMT2PCA/DAmplifierSlit1VacuumPowerspectrumofhighharmonics800nm,1015W/cm2,neontarget750-1100nm(4.5fs)----(100TW)1020W/cm23.51016W/cm21012bar1bar1021gg109Gauss0.5Gauss………Femtochemistry----NobelPrize1999TheRoyalSwedishAcademyofScienceshasawardedthe1999NobelPrizeinChemistrytoProf.AhmedH.Zewail(CIT),forshowingthatitispossiblewithrapidlasertechniquetoseehowatomsinamoleculemoveduringachemicalreaction.TheAcademy’scitation:Forhisstudiesofthetransitionstatesofchemicalreactionsusingfemtosecondspectroscopy——1999NaINaINaIExperimentalobservationofcoherentvibration(wave-packetmotion)probepointNaDFsLaser-InducedFissionApetawattlaserbeam(1020W/cm2)strikesagoldfoilresultsin(1)thehighestenergyelectrons(upto100Mev)(2)thefirstlaser-inducedfission(3)thefirstcreationofantimatter(positrons)usinglight238U92Kr+143Ba+3e+FastIgnitionConceptofICF(ICF---inertialconfinementfusion)—Nature,Vol.412,697.2001FlapcutbyfslaserpulseFlapcutbyamechanicalmicrokeratomeCanultrafstlasermeetthetransitionfromresearchtoolsintotherealworldapplication?Optics&PhotonicsNews1999“Ultrafastlaserwillfindapplicationsinareasrequiringdelicatework.”Clark-MXRPresidentPhilippeBado