Laser-assisted elastic electron scattering from helium

We report measurements of the differential cross section for scattering of electrons, from helium, with energies in the range 1–20 eV through scattering angles of 14°–140° in the presence of a high-intensity carbon dioxide laser. These results were obtained with beam geometries for which the Kroll–Watson approximation, normally applied to these types of measurements, predicts zero cross sections. The cross sections reported are not zero but confirm similar experiments with argon as the scattering centre.