Abstract

A major implication of the remarkable data^/1-3/ on multiple ionization of many electron atoms in intense laser pulses is the unusually strong coupling strength at UV and infrared frequencies. Luk et al.^/2/ appear to have been the first to envisage a giant dipole or multipole excitation of atoms, in the present context. The purpose of this paper is to give a many-body non-perturbative analysis (using a generalization of a method of Tomonaga^/4/ within the random phase approximation) of an N-electron atomic Hamiltonian coupled to a laser pulse and to demonstrate the existence of laser driven colletive dipole excitations of noble gas atoms. We also determine the photon absorption cross-sections due to this process. It is shown that the dipole operator of a many-electron atom can execute quantum oscillations with a distribution of fundamental frequencies and that the laser excites preferentially the mode whose frequency is resonant with the laser frequency. These modes appear essentially in the outer region of the atomic charge distribution, both at 193 nm and 1064 nm laser wavelengths. It is found, for example, for Xe that the 5p⁶ and the 5s² sub-shells alone contribute virtually completely to the resonant modes; all the other shells contributing less than 0.1%.

© 1986 Optical Society of America