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 degrees -140 degrees 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.