Proton-hydrogen-atom scattering in a nearly resonant laser field

We consider proton scattering from hydrogen atoms in the presence of a laser beam that resonantly (or nearly resonantly) excites the hydrogen atoms from the 1s to the 2p state. The laser beam propagates in a direction perpendicular to the proton beam, and it is linearly polarized, with polarization either parallel (longitudinal) or perpendicular (transverse) to the direction of incidence of the proton. We allow the collision to couple the 1s, 2s, and 2p states and we treat the interaction of the laser with the atom in the two-state rotating-wave approximation. We have calculated the integrated cross section, σ(2s), for excitation of the 2s state. We find that the laser enhancement of σ(2s) is small for longitudinal polarization, but for transverse polarization σ(2s) varies rapidly with laser intensity, and in the intensity range 10⁹-10¹⁰ W/cm² σ(2s) is of the order of 100 times larger than its value in the field-free case.