Laser-assisted inelastic electron-atom collisions

We study the inelastic scattering, accompanied by the transfer of L photons, of fast electrons by hydrogen and helium atoms in the presence of a laser field. A detailed analysis is made of the excitation of the n=2 and n=3 states of atomic hydrogen, and of the 1 ¹S--2¹S and 1 ¹S--2 ¹P transitions in helium. It is shown that the ``dressing'' effect due to the dipole distortion of the target by the laser field produces important modifications of the cross sections at small momentum transfers for S-S and S-D transitions. However, this dressing effect is reduced in the case of S-P transitions. Our results exhibit qualitative differences from the case of laser-assisted elastic collisions; this is mainly due to the possibility of intermediate resonances in the laser-atom interaction during the collision event.