Electron-hydrogen collisions in the presence of a laser field: one-photon excitation

Abstract

The authors present a new calculation of the excitation cross sections of atomic hydrogen by the impact of fast electrons in the presence of a laser field. The computation is performed within the framework of perturbation theory to lowest non-vanishing order. In contrast with previous work, the authors do not restrict themselves to the Bethe-Born approximation for the electron-atom interaction; this opens many new channels for the scattering process. The Coulomb Green's function is represented accurately and efficiently in either of two L2 basis sets, one of Slater-Laguerre type and one Sturmian, rather than as a sum and integral over intermediate states. One result is to show that the Bethe-Born approximation does not provide reliable estimates of the cross sections for such processes. Another interesting feature of the authors' model is the prediction of deep minima in the cross sections. Their origin, as well as the magnitudes of the different terms contributing to the overall transition amplitudes, is discussed.