超快光學相干控制PPT學習教案

1、會計學1超快光學相干控制超快光學相干控制C = catalystMuch can be done, but not everything wed like.第1頁/共25頁But its not so easy! Theres a lot more to it.nA long-held dream of chemists. Its now coming true. Shaped ultrashort pulses are the key.Coherent control slides mostly thanks to Gustav Gerber, University of Wurzberg,

2、 GermanyMargaret Murnane and Henry Kapteyn, JILARobert Levis, Temple University第2頁/共25頁IVR occurs on a few-fs time scale, so long pulses excite entire molecule, and the weakest bond breaks, no matter which bond was excited.Excite one bondA few fs later, however, the entire molecule is vibrating.The

3、bond vibrates第3頁/共25頁Surprisingly, these simple methods often work, but they are not general.第4頁/共25頁Can an ultrashort pulse cause a molecule to vibrate in such a way as to break the bond of our choice?第5頁/共25頁MoleculeE-field of LaserPerturbed SystemWave-functionPotentialThe pulse electric field per

4、turbs the molecule and potentially dissociates it.The trick is to compute the required pulse electric field.Wave-functionPotential第6頁/共25頁H H system = H H molecule + H H radiation + H H interactionH H radiationknown H H moleculesmall molecules: approximatelarge molecules: unknownH H interactionweak

5、field: knownstrong field: unknownfiEFirst, we need to know the complete Hamiltonian for the molecule and radiation:For all but the simplest molecules, its hopeless to solve the problem.第7頁/共25頁第8頁/共25頁第9頁/共25頁This algorithm was developed for computer optimization, but, for coherent control, it can b

6、e implemented as part of an experiment.第10頁/共25頁第11頁/共25頁第12頁/共25頁Shaped PulseCO2CCl4CCl2OReaction under studyMurnane and Kapteyn, University of Colorado第13頁/共25頁H3CCH3COH3CCH3CO+Levis and coworkersAcetone can be broken into various pieces. A laser pulse could help. 25 H3C-C-CH3+=20151050Normalized

7、ion signal6050403020100Mass, amu M-15+M-30+ H2O+CH3+C+C+H+O2+(Acetone+)OMass spectrumH3CCH3COCH3CO+第14頁/共25頁 6040200Normalized Ion IntensityAcetone+CH3CO+generation221030Mass (amu)70605040302010Goal: Optimize CH3CO+ at 43 amuScience 2001, 292, 709 Levis and coworkers第15頁/共25頁Science 2001, 292, 709 L

8、evis and coworkers=10080604020CH3CO+ Signal2520151050Generation NumberH3C-C-CH3CH3CO + CH3O第16頁/共25頁COCH3COCH3+COCH3+Different pulse shapes can optimize different photo-fragments.Levis and coworkers1.00.80.620151050GenerationRatio:C7H5O/C6H5 Normalized ion intensity and ratio第17頁/共25頁Normal

9、ized ion intensity and ratioCOCH3+COCH3+GenerationRatio: C6H5/C7H5O 2.22.01.21.020151050COCH3100 kcal/mole85 kcal/moleLevis and coworkersOptimizing the phenyl fragment yield also works.第18頁/共25頁COCH3+COCH3+COCH3enhancesuppressLevis and coworkersThe pulse that maximizes the ratio of the two

10、fragments.Interestingly, a very simple pulse maximizes the phenyl radical (but not the ratio).Delay (fs)-150-75075150395420Wavelength (nm)SHG FROG trace第19頁/共25頁to POLLIWOG apparatusinput pulse第20頁/共25頁第21頁/共25頁Gerber and coworkers第22頁/共25頁It works, not only in the gas phase, where dephasing times a

11、re long, but also in the liquid phase. This is potentially very useful!Almost any wavelength will do, as high intensity broadens the energy levels significantly, making all processes effectively resonant.Rabitz has shown that it is robust and should occur for essentially all systems.By determining t

12、he precise field that optimizes the desired product, we also learn about the molecule.Coherent control has applications far beyond chemistry.第23頁/共25頁(1) Fluorescence spectrum manipulation (Wilson, 1997)(2) Atomic excitation tailoring (Bucksbaum, 1999)(3) Vibrational excitation tailoring in polymers

13、 (Motzkus, 2002)(4) Molecular fragmentation selectivity (Gerber, 1998; Levis & Rabitz, 2001)(5) Molecular rearrangement selectivity (Levis & Rabitz, 2001)(6) Chemical discrimination (Gerber, 2001)(7) High harmonic X-ray tailoring (Murnane & Kapteyn, 2000)(8) Ultrafast solid-state optical switching (Keller, 2000)(9) Distortion-free transmission of pulses in