Multiphoton ionization in superintense, high-frequency laser fields. Stabilization of atomic hydrogen in linearly polarized fields

Publisher Website
Google Scholar
Abstract
This is the second of two papers studying the multiphoton ionization (MPI) in superintense, high-frequency laser fields. They are based on a general iteration scheme in increasing powers of the inverse frequency. To lowest order in the frequency, i.e., the high-frequency limit, the atom is stable against decay by MPI, though distorted. To next order in the iteration, an expression for the MPI amplitude was obtained. In our first paper [preceding paper, Phys. Rev. A 44, 2160 (1991)], an alternative expression for the MPI amplitude was obtained for atomic hydrogen, which is substantially simpler, though somewhat less accurate. In the present paper, we study its consequences for the case of atomic hydrogen in superintense, linearly polarized fields with the emphasis on the ground state. Special attention is paid to the case in which the de Broglie wavelength of the photoelectrons is small with respect to the amplitude of oscillation of the (distorted) electronic cloud. Most importantly, the total decay rate decreases with increasing intensity at given (high) frequency (‘‘high-intensity stabilization’’). This condition defines a radiation regime which yields features in sharp contrast to those obtained in weak fields. The angular distributions of photoelectrons are found to be characterized by rapid oscillations with the polar angle, arising from a peculiar way in which outgoing electron waves interfere.