Semiclassical Multi-Mode Floquet Theory and Non-Adiabatic Approximation Quasi-Energy Method for Intense Field Multiphoton Processes

Abstract

The use of the (single-mode) semiclassical Floquet theory [1,2] for nonperturbative treatments of the multiphoton dynamics of finite-level systems, involving periodic time-dependent Hamiltonians, has attracted considerable attention in the last few years. A detailed review of the theoretical investigations for two-level systems has been given by Dion and Hirschfelder [2]. Recently the conventional (single-mode) finite-level Floquet theory [1,2] has been extended to infinite-level (to include both bound as well as continuum states) non-Hermitian Floquet or complex quasi-energy theories [3–6], employing the use of complex-coordinate transformation [7] and L2-continuum discretization. This yields practical techniques for the study of intense field multiphoton ionization (MPI) of atoms [3], Stark-Zeeman [4] and laser-Zeeman [5] effects as well as multiphoton dissociation (MPD) of small molecules [6], using entirely only bound-state technology. In this paper, two new developments in Floquet theory, namely, the generalized multi-mode Floquet theory as well as a non-adiabatic quasi-energy method will be briefly presented.