Abstract

We will review computational and physical aspects of the ionization of an atom by N photons with N>P, where P is the minimum number of photons required to ionize the atom. In perturbation theory the matrix element, M^(N), for N-photon absorption can be decomposed as M^+(N) + M^−(N), which results from the decomposition of the stationary wave of the emergent photoelectron into its outgoing ( + ) and ingoing (−) parts. Each of the M^±(N)are N-dimensional integrals over N radial coordinates r_i, i=1,…,N. Although these integrals are not formally convergent for N>P, the integrand of M^+(N) consists of functions that either decay exponentially or are outgoing waves for r_i~∞.

© 1986 Optical Society of America