Abstract

The study of atoms in intense laser fields is the subject of significant theoretical interest due to recent, surprising experimental results which have included ion-, electron-, and photoemission spectroscopy. The results include unexpectedly high stages of ionization (multiple ionization), absorption of an excess of photons during the ionization process (above threshold ionization), and the emission of surprisingly intense, short-wavelength radiation (harmonic conversion). To some extent all such observations have been attributed initially to the breakdown of perturbation theory. To establish whether this is the case, we have chosen a completely nonperturbative approach to study the dynamics of excitation of atoms in strong fields. Thus, we directly solve the time-dependent Schrodinger equation as accurately as possible for a laser pulse shape which can mimic real experimental conditions. For multielectron systems we employ the time-dependent Hartree-Fock TDHF representation of the wave function.¹ For a range of intensities we have found that a single-active-electron approximation to the TDHF equations can give quite good results in comparison with experiments on many systems for ionization rates² and photon emission.³

© 1989 Optical Society of America