A simple model of ionization, capable of dealing with arbitrarily strong laser fields, is discussed. A model ‘‘atom,’’ consisting of a rectangular well potential of finite depth is perturbed by a train of δ kicks that are alternating in sign. The results of exact (numerical) calculations are compared with those obtained neglecting continuum-continuum transitions. Both the ionization rate and the photoelectron spectra are discussed. Neglecting continuum-continuum transitions leads to good results for the ionization rate which is well approximated by the low-field perturbative expression up to very strong fields. On the contrary photoelectron spectra are sensitive to a detailed form of continuum-continuum matrix elements (both to their singular and regular parts).

• Received 31 March 1987

DOI:https://doi.org/10.1103/PhysRevA.36.4311