Laser assisted free-free scattering: a test of the Kroll-Watson approximation for different targets

In previous work we reported on experiments that examined electron-helium scattering in the presence of an Nd:YAG laser field of 1.17 eV photons. We tested the Kroll-Watson approximation (KWA)\footnote{N. M. Kroll and K. M. Watson, Phys. Rev. A 8, 804 (1973)} for one photon emission, over a range of incident electron energies 50~eV $\to$ 350~eV at fixed laser polarization,\footnote{B. A. deHarak, L. Ladino, K. B. MacAdam and N. L. S. Martin, Phys. Rev. A {\bf 83}, 022706 (2011)} and also the for the effect of varying the laser polarization direction within a plane perpendicular to the scattering plane.\footnote{http://meetings.aps.org/link/BAPS.2013.DAMOP.D1.150} Both these experiments were in good agreement with the KWA. We are currently carrying out measurements of one, two, and three photon absorption, in three different targets, He, Ar, and N$_2$. The KWA predicts that the results should be target independent, since the approximation assumes negligible photon-target interaction. We will present the results of experiments carried out at different incident electron energies.