K. J. LaGattuta

QUASICLASSICAL MODELLING OF HELIUM DOUBLE PHOTOIONIZATION

We applied the method known as fermion molecular dynamics (FMD) to the description of a helium atom interacting with a short pulse of intense, long-wavelength laser radiation, for both linear and circular polarization. We describe the results of these calculations, insofar as they bear on the question of the mechanisms leading to double electron ejection. In the case of linear polarization, boomeranging trajectories leading to double ionization were observed at all laser intensities above threshold. The probability of occurrence was low, and almost independent of laser intensity. However, very near to threshold, boomeranging trajectories leading to double ionization were found to occur with a probability comparable to that for all other independent electron (sequential) processes. This produced a shoulder in the curve of double ionization probability versus laser intensity. The size of this shoulder was found to depend on laser wavelength and pulse length. No such trajectories were found for circular polarization.

Photoionization of atoms described by Fermi Molecular Dynamics: toward a firmer theoretical basis

The application of Fermi Molecular Dynamics (FMD) to the modeling of the photoionization of atoms by a short pulse of long wavelength laser radiation is examined in detail. Depression of the single ionization threshold to values of the electric field strength below the classical over-the-barrier threshold, a common occurrence in FMD, is shown to arise from the preexcitation of bound electrons into a continuum of unphysical low-lying excited states. A connection is made to analogous calculations performed with the quantum Hamilton-Jacobi equation, in which the time-dependent quantum potential (

Multiple ionization of argon atoms by long-wavelength laser radiation: a fermion molecular dynamics simulation

Q

Quasiclassical Approach to Ionization of Atoms by Strong Laser Pulses: Comparison with the “Simpleman’s” Models and Newtonian Dynamics

) plays a role similar to that played in FMD by the so-called Heisenberg potential (V H). Replacement of (V H) by Q in the FMD equations of motion results in a large reduction in the number of excitations to unphysical bound states, while producing no essential change in the photoionization probability.

Ionization of helium by a short pulse of radiation: A Fermi molecular-dynamics calculation

We applied the method known as fermion molecular dynamics to the description of an isolated argon atom interacting with a short pulse of intense, long-wavelength laser radiation, for both linear and circular polarization. We discuss the results of these calculations, insofar as they bear on the mechanisms leading to the production of high-ionic-charge states during laser-atom interaction.

Laser effects in photoionization. II. Numerical solution of coupled equations for atomic hydrogen.

The current paper is a continuation of our previous paper [1], in which we proposed to study electron-electron correlations in the quasiclassical model of Kirschbaum and Wilets (also called Fermi Molecular Dynamics (FMD)) [2] with respect to multipho-ton ionization. This model has been already implemented in the paper of Wasson and Koonin [3] for the study of multiphoton ionization rates for multielectron atoms. In the present paper we provide the comparison between quasiclassical FMD and purely classical models for multiphoton ionization. Here, we concentrate on the second simplest quantum system, the He atom.