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. A49, 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.