Molecular dynamics and control following excitation with an ultra-short intense laser pulse

Lou, Nan-Quan; Nyman, Gunnar

doi:10.1016/j.chemphys.2003.12.024

Cited by 10 publications

(1 citation statement)

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“…In numerical simulations one frequently uses a model in which it is assumed that the orientation of the molecule is fixed or "clamped" with respect to the direction of the ͑linearly polarized͒ field throughout the interaction time. [1][2][3][4][5][6][7][8][9] In their review on stateselective dynamics, 1 Korolkov et al conclude that "more advanced model investigations" should include molecular rotation. In fact, free molecules do rotate and are statistically distributed over the quantum rotational states, and even in the condensed phases they may have a random orientation.…”

Section: Introductionmentioning

confidence: 99%

Rotational averaging and optimization of laser-induced population transfer in molecules

Leuven

Persico

2006

The Journal of Chemical Physics

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The dynamics of a molecule subject to a short laser pulse is investigated, with focus on the averaging over initial rotational states and on the optimization of laser parameters for the efficient population transfer between vibrational and electronic states. A relation is established between final-state populations obtained with a fixed orientation and those based on a full treatment of the rotational degrees of freedom. In the short-pulse approximation, rotational averaging amounts to integrating the fixed molecule results over all orientations. The theory is applied to a variety of model systems and verified with numerical calculations using Gaussian pulses. We calculate target state populations with three procedures, optimizing the laser pulse for a fixed orientation without orientational averaging, averaging without changing the laser parameters, and reoptimizing the parameters after averaging. The analysis of the two-level system provides a reference for the order of magnitude of the effects of averaging. The three-level system brings out the relevant role of the geometry of polarization vectors and transition dipoles. The multiphoton excitation of a Morse oscillator shows the importance of taking into account the dependence of resonance frequencies on the laser intensity. Within a proton transfer model we discuss the results obtained with and without chirping and we show that "optimizing after averaging" can be as effective as choosing a more refined pulse shape.

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