Atoms in multi-mode radiation fields

Abstract
The Floquet formalism for atoms in semiclassical monochromatic radiation fields has recently been extended to the multi-mode case by Chu and co-workers (1983). The authors generalise a version of the Floquet formalism for the single-mode case originated by Howland to the multi-mode situation and give expressions for multi-photon ionisation amplitudes in the spirit of time-independent scattering theory. A comparison is made with the corresponding second quantised formalism.