超快光学相干控制PPT学习教案

1、会计学1超快光学相干控制超快光学相干控制C = catalystMuch can be done, but not everything wed like.第1页/共25页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页/共25页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页/共25页Surprisingly, these simple methods often work, but they are not general.第4页/共25页Can an ultrashort pulse cause a molecule to vibrate in such a way as to break the bond of our choice?第5页/共25页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页/共25页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页/共25页第8页/共25页第9页/共25页This algorithm was developed for computer optimization, but, for coherent control, it can b

6、e implemented as part of an experiment.第10页/共25页第11页/共25页第12页/共25页Shaped PulseCO2CCl4CCl2OReaction under studyMurnane and Kapteyn, University of Colorado第13页/共25页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页/共25页 6040200Normalized Ion IntensityAcetone+CH3CO+generation221030Mass (amu)70605040302010Goal: Optimize CH3CO+ at 43 amuScience 2001, 292, 709 Levis and coworkers第15页/共25页Science 2001, 292, 709 L

8、evis and coworkers=10080604020CH3CO+ Signal2520151050Generation NumberH3C-C-CH3CH3CO + CH3O第16页/共25页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页/共25页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页/共25页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页/共25页to POLLIWOG apparatusinput pulse第20页/共25页第21页/共25页Gerber and coworkers第22页/共25页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页/共25页(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