Optimization of Wave Packet Coefficients in Li2 Using an Evolutionary Algorithm: the Role of Resonant and Non-Resonant Wavelengths

Published

January 1, 2002

Author(s)

J B. Ballard, H U. Stauffer, Z Amitay, S R. Leone

Abstract

Using feedback and an Evolutionary Algorithm (EA), the weak field pump-probe photoionization single at a single time delay is optimized inLi₂. A single launch state is prepared via excitation with a cw laser, from which a pump pulse excites a superposition of two rotational states on an excited electronic potential energy curve: E ¹Sigma_g⁺(Ņ_E=9, J_E=27 and 29). The EA modifies the phase pattern versus wavelength of the ultrafast pump pulses using a pulse shaper with a 128 pixel Liquid Crystal Spatial Light Modulator (LC-SLM). Limitations of frequency resolution for the pulse shaper create an effective temporal window in which pulses can be shaped. Optimization of the photoionization signal at pump-probe time delays outside of this temporal pulse shaping window involves phase shifts of only the two frequencies resonant with the transition to the wave packet states, effectively introducing a phase shift in the wave packet recurrences. For pump-probe tiem delays inside the pulse shaping window, optimization of the photoionization shows the influence of not only resonant but also non-resonant wavelengths. In this regime, the phase shift of wave packet recurrences as well as the time-dependent wave packet amplitude coefficients are opitmized. First order time dependent perturbation theory is used to explain the mechanism by which the photoionization is maximized. These experiments are the first to use an optimization routine as a tool to identify a variety of simultaneous mechanisms that underlie the maximization of a process.

Citation

Journal of Chemical Physics

Volume

116

Issue

No. 4

Pub Type

Journals

Keywords

Evolutionary algorithm, optimization, wave packet

Citation

Ballard, J. , Stauffer, H. , Amitay, Z. and Leone, S. (2002), Optimization of Wave Packet Coefficients in Li₂ Using an Evolutionary Algorithm: the Role of Resonant and Non-Resonant Wavelengths, Journal of Chemical Physics (Accessed July 27, 2024)