Potential barrier effects in high-order harmonic generation by transition-metal ions

The experimental finding of significant enhancement or suppression of particular harmonics generated by the ionic component of laser-produced plasmas of transition-metal atoms is explained theoretically in terms of the standard three-step scenario for strong-field harmonic generation, taking into account the potential barrier effects that lead to a strong 3p -> 3d electric dipole transition that dominates the photoionization cross sections of the outer subshells of those ions.