Resonant coherent excitation in atom-surface scattering at grazing incidence

Within a semiclassical approximation the excited-state density matrix is calculated for a resonant 1s → 2p transition in a hydrogen-like projectile. The resonant coherent excitation process is induced by the periodic surface potential seen by the particle during its surface passage at grazing incidence. We find an anisotropic magnetic sublevel population which yields a high degree of polarization in a subsequent photon emission. The dependence of the Stokes parameter on both the relative orientation between the beam velocity v and the crystal axes and the surface potential decaying along the surface-normal are studied. (orig.)