Laser-assisted electron-impact ionization of atoms

Fast, 1 keV electron-helium collisions performed in an intense (4×1012 W/cm2), non-resonant laser field were investigated realizing the first experiment for laser-assisted ionization. The resulting double- and triple-differential cross-sections for the single ionization show significant differences in comparison to the field-free cross-sections. Our quantum-mechanical calculation, using a First-Born approximation (FBA) to describe the collision and Volkov states for the continuum electrons, cannot explain the measured cross-sections.