Free-free experiments: dressed-atom effects during inelastic electron scattering*

Free-free experiments investigate the absorption or emission of radiation during the collision of charged particles with atoms and molecules. The first experimental observation of dressed-atom effects -- due to the electric field of the laser -- during the elastic scattering of electrons by Xe were reported by Morimoto {\em et al}.\footnote{Y. Morimoto, R. Kanya, and K. Yamanouchi, Phys.\ Rev.\ Lett.\ {\bf 115}, 123201 (2015)} Their results were compared with an analytical expression by Zon that contains the electric dipole polarizability $\alpha$ of the target.\footnote{B. A. Zon, Sov. Phys. JETP 46(1), 65 (1977)} We are investigating dressing effects for {\em inelastic} electron scattering in the presence of a Nd:YAG laser; specifically we are investigating electron-impact excitation of the lowest excited states of He and Ar. Zon's expression is not valid for {inelastic} scattering so we have developed an equivalent inelastic expression. We will give the results of a simple calculation for dressing effects for the excited states of He, and will give a progress report on our experiments.