超快光学-第16章-相干控制.ppt

CoherentControl CoherentControlattemptstocontrolachemicalreactionwithlight usuallyacleverlyshapedultrashortlaserpulse Whyit shard IVR Usingshapedpulsesandaniterativeapproach Conventionalmethodsofchemicalcontrol Muchcanbedone butnoteverythingwe dlike CoherentControl ChemicalreactionsproceedinamannerdeterminedbythemolecularHamiltonian Whatifwe dliketochangethisandmakedifferentproducts Bringinalightfrequencytoexciteabondwe dliketobreak Butit snotsoeasy There salotmoretoit Along helddreamofchemists It snowcomingtrue Shapedultrashortpulsesarethekey CoherentcontrolslidesmostlythankstoGustavGerber UniversityofWurzberg GermanyMargaretMurnaneandHenryKapteyn JILARobertLevis TempleUniversity IVRoccursonafew fstimescale solongpulsesexciteentiremolecule andtheweakestbondbreaks nomatterwhichbondwasexcited Exciteonebond Afewfslater however theentiremoleculeisvibrating IntramolecularVibrationalRedistribution Thebondvibrates Single parametercontrol Surprisingly thesesimplemethodsoftenwork buttheyarenotgeneral Coherentcontrol Usingshapedultrashortpulsestocontrolthereaction Cananultrashortpulsecauseamoleculetovibrateinsuchawayastobreakthebondofourchoice Thephysicsofcoherentcontrol Molecule E fieldofLaser PerturbedSystem Wave function Potential Thepulseelectricfieldperturbsthemoleculeandpotentiallydissociatesit Thetrickistocomputetherequiredpulseelectricfield Tryingtodothetheoryforcoherentcontrol Hsystem Hmolecule Hradiation Hinteraction Hradiation known First weneedtoknowthecompleteHamiltonianforthemoleculeandradiation Forallbutthesimplestmolecules it shopelesstosolvetheproblem Wecouldtrytosolvetheproblemtheoretically butit seasiertojustdoititerativelyinthelab Pulse shapingisimportantforcoherentcontrol Geneticalgorithmforcoherentcontrol Thisalgorithmwasdevelopedforcomputeroptimization but forcoherentcontrol itcanbeimplementedaspartofanexperiment Ageneticalgorithmcanminimizethepulselength Usingalearningalgorithmtoperformcoherentcontrol Coherentcontrolofasimplegasphasereaction ShapedPulse CO2 CCl4 CCl2O Reactionunderstudy MurnaneandKapteyn UniversityofColorado H3C CH3 C O Coherentcontrolwithacetone gasphase Levisandcoworkers Acetonecanbebrokenintovariouspieces Alaserpulsecouldhelp CH3CO 60 40 20 0 NormalizedIonIntensity Acetone CH3CO generation 22 10 3 0 70 60 50 40 30 20 10 Goal OptimizeCH3CO at43amu Optimizingoneacetonephoto fragment Science2001 292 709 Levisandcoworkers Maximizationoftherelevantphoto fragmentoccursrapidly Science2001 292 709 Levisandcoworkers 100 80 60 40 20 CH3CO Signal 25 20 15 10 5 0 GenerationNumber H3C C CH3 CH3CO CH3 O C O CH3 C O CH3 C O CH3 Manipulatingthedissociationyieldsinacetophenone Differentpulseshapescanoptimizedifferentphoto fragments Levisandcoworkers 1 6 1 4 1 2 1 0 0 8 0 6 Generation Ratio C7H5O C6H5 Normalizedionintensityandratio Normalizedionintensityandratio Generation Ratio C6H5 C7H5O 2 2 2 0 1 8 1 6 1 4 1 2 1 0 C O CH3 100kcal mole 85kcal mole Reversingtheratio Increasingthephenylyield Levisandcoworkers Optimizingthephenylfragmentyieldalsoworks enhance suppress Whatdothesepulseslooklike Levisandcoworkers Thepulsethatmaximizestheratioofthetwofragments Interestingly averysimplepulsemaximizesthephenylradical butnottheratio SHGFROGtrace Moleculesarenotisotropic sopulsepolarizationshapingisimportant Acomplexpolarization shapedpulse Coherentpolarizationcontrolofacomplexmoleculeinthegasphase Gerberandcoworkers Coherentcontrolishere Itworks notonlyinthegasphase wheredephasingtimesarelong butalsointheliquidphase Thisispotentiallyveryuseful Almostanywavelengthwilldo ashighintensitybroadenstheenergylevelssignificantly makingallprocesseseffectivelyresonant Rabitzhasshownthatitisrobustandshouldoccurforessentiallyallsystems Bydeterminingtheprecisefieldthatoptimizesthedesiredproduct wealsolearnaboutthemolecule Coherentcontrolhasapplicationsfarbeyondchemistry Successfulclosed loopcoherentcontrolexperimentsinphysicsandchemistry 1 Fluorescencespectrummanipulation Wilson 1997 2 Atomicexcitationtailoring Bucksbaum 1999 3 Vibrationalexcitationtailoringinpolymers Motzkus 2002 4 Molecularfragmentationselectivity Gerber 1998 Levis Rabitz 2001 5 Molecularrearrangementselectivity Levis Rabitz 2001 6 Chemicaldiscrimination Gerber 2001 7 HighharmonicX raytailoring Murnane Kapteyn 2000 8 Ultrafastsolid stateopticalswitchin