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 scatterin g processes in the presence of a laser field in view of the recent exp eriments by Wallbank and Holmes. In these experiments a large discrepa ncy between the observed data for small-angle scattering and the on-sh ell Kroll-Watson formula was reported. We show in the present work tha t the off-shell effects are not responsible for this discrepancy by pr esenting results for the differential cross sections obtained, using t he off-shell low-frequency approximation and the [1, 1] Pade approxima tion. We model the scattering from helium and argon atoms by the scatt ering on a Yukawa-type potential. We show, using some examples, that h igher laser field frequencies and intensities are necessary for obtain ing observable off-shell-effects. We also comment on possibilities of explaining the Wallbank and Holmes results. For one of these possibili ties-double scattering-we compute, using our simple model, the relativ e differential cross sections and obtain a qualitative agreement with the experiments of Wallbank and Holmes, both for helium and argon.