Role of surface interactions in beam-foil excited-state formation

Polarization measurements have been performed on radiation emitted by ${\mathrm{He}}^{+}$ ions (468.6 nm) in transmission (beam foil) and reflection (grazing incidence) geometries, with use of both carbon foil and silicon single-crystal targets. Comparison of the results of the two geometries and the two different targets indicates that the excited-state formation occurs at the exit surface. The impact of these results on current theories is discussed.