e-H collisions in a resonant monochromatic or bichromatic laser field

The elastic 2s-->2s and inelastic 2l-->3l' laser-assisted collision of hydrogen with fast incident electrons is studied, by applying the nonperturbative Born-Floquet theory. The embedding monochromatic or 3 + 1'' bichromatic linearly polarized field of moderate intensity tunes the n=2 and n=3 levels into one-photon resonances. A peculiarity of the laser-assisted e-H collision involving levels with ngreater than or equal to3 is that cross sections corresponding to no photon exchange with the field do not reduce to the field-free cross sections in the I-->0 limit. In addition, structures in the cross sections like two separate peaks in the resonance vicinity are observed, resulting from interferences between different resonant excitation virtual pathways from an initial to the final state. An increase of intensity of the monochromatic field by two orders of magnitude has the consequence of attenuating resonant structures in the cross sections. For rather moderate intensities of both components of the bichromatic field, narrow multiphoton resonances induced by the lower-frequency field appear, superimposed on wings of broad resonances brought in by the higher-frequency field. The overall effect on the cross sections for e-H scattering resulting from relative-phase variation of the resonant moderate-intensity bichromatic field is small.