Control of nitromethane photoionization efficiency with shaped femtosecond pulses |
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Authors: | Roslund Jonathan Shir Ofer M Dogariu Arthur Miles Richard Rabitz Herschel |
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Institution: | Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA. jroslund@princeton.edu |
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Abstract: | The applicability of adaptive femtosecond pulse shaping is studied for achieving selectivity in the photoionization of low-density polyatomic targets. In particular, optimal dynamic discrimination (ODD) techniques exploit intermediate molecular electronic resonances that allow a significant increase in the photoionization efficiency of nitromethane with shaped near-infrared femtosecond pulses. The intensity bias typical of high-photon number, nonresonant ionization is accounted for by reference to a strictly intensity-dependent process. Closed-loop adaptive learning is then able to discover a pulse form that increases the ionization efficiency of nitromethane by ~150%. The optimally induced molecular dynamics result from entry into a region of parameter space inaccessible with intensity-only control. Finally, the discovered pulse shape is demonstrated to interact with the molecular system in a coherent fashion as assessed from the asymmetry between the response to the optimal field and its time-reversed counterpart. |
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