Multiphoton and above-threshold detachment computed for a model negative ion and compared with perturbation theory

Abstract

Multiphoton excitation of a model negative ion is studied. The model has only a single bound level, and we choose a photon frequency appropriate to five-photon photodetachment (before ponderomotive threshold shifts). Both of these characteristics are compatible with multiphoton detachment studies of the hydrogen negative ion made with CO2 laser radiation. We study the model in a discretized energy basis in order to study independently the influence of bound–continuum (B–C) and continuum-continuum (C–C) dipole matrix elements on the multiphoton detachment process. Because the energy-level structure of the model (and also of negative ions generally) is relatively simple compared with that of atoms, we are able to investigate a number of questions in some detail, using either perturbation theory or exact numerical solutions to Schrödinger’s equation. Interesting consequences are the explicit identification of an interference between B–C-dominated and C–C-dominated detachment channels and the emergence of energy-nonconserving contributions to above-threshold electron spectra.