Electron-helium scattering in a 1.17 eV laser field: The effect of polarization direction

We report measurements of one-photon emission during the elastic scattering of electrons by He atoms through 90 degrees in the presence of 1.17 eV photons from a Nd:YAG laser. The incident energy of the electrons was in the range 30-200 eV and the linear polarization direction of the laser was varied over 180 degrees in the plane, perpendicular to the scattering plane, that contains the momentum transfer direction. Our results are perfectly consistent with the Kroll-Watson approximation. In particular, we see no evidence of free-free transitions when the polarization is perpendicular to the momentum transfer direction.