Comparison of quasi-classical and quasi-static quantum approaches to the ionization of helium by a circularly polarized laser field

Employing the quasi-classical Fermi molecular dynamics (FMD) method, we find no evidence for the existence of a nonsequential double-ionization mechanism for helium interacting with a pulse of circularly polarized, high-intensity laser radiation. This contrasts with our earlier research, for linearly polarized laser light [Phys. Rev. A 49, R12 (1994)], in which effects of the nonsequential double ionization of helium were noted. We also compute emitted-electron kinetic energy spectra by FMD and compare these with spectra derived from a quasi-static tunneling model calculation. In this context we discuss the applicability of the FMD approach to simulations of the photoionization of multielectron systems by intense pulsed laser fields. (C) 1996 Optical Society of America