Off-shell low-frequency approximation for potential scattering in a laser field: Comparison with the Wallbank and Holmes experiments

We investigate the influence of the off-shell effects on the scattering processes in the presence of a laser field in view of the recent experiments by Wallbank and Holmes. In these experiments a large discrepancy between the observed data for small-angle scattering and the on-shell Kroll-Watson formula was reported. We show in the present work that the off-shell effects are not responsible for this discrepancy by presenting results for the differential cross sections obtained, using the off-shell low-frequency approximation and the [1, 1] Pade approximation. We model the scattering from helium and argon atoms by the scattering on a Yukawa-type potential. We show, using some examples, that higher laser field frequencies and intensities are necessary for obtaining observable off-shell-effects. We also comment on possibilities of explaining the Wallbank and Holmes results. For one of these possibilities-double scattering-we compute, using our simple model, the relative differential cross sections and obtain a qualitative agreement with the experiments of Wallbank and Holmes, both for helium and argon.