Effects of a laser field on electron-atom ionizing collisions

The presence of a laser field is found to alter significantly the shape of the angular distribution of ejected electrons in electron-atom ionizing collisions when photon exchanges occur. Laser electric fields parallel to the primary electron transferred momentum (${\overrightarrow{\mathrm{E}}}_L\parallel {\overrightarrow{\mathrm{K}}}_{\mathrm{if}}$) increase the number of secondary electrons ejected in the backward direction (with respect to ${\overrightarrow{\mathrm{K}}}_{\mathrm{if}}$). Laser electric fields perpendicular to ${\overrightarrow{\mathrm{K}}}_{\mathrm{if}}$ double the peaks present in the field-free angular distribution and rotate them symmetrically in opposite directions from the ${\overrightarrow{\mathrm{K}}}_{\mathrm{if}}$ axis towards the ${\overrightarrow{\mathrm{E}}}_L$ axis. Calculations are presented for ionization events accompanied by one-photon absorption in a coplanar asymmetric geometry.