Direct multiphoton transitions to highly excited two-electron states

Abstract
Photoelectron energy spectra from multiphoton ionization of magnesium reveal that direct nine or ten-photon transitions to 4p and possibly 5p thresholds are taking place around 586 nm and about 1012 W cm-2. Lineshapes indicate that such transitions are enhanced by the intermediate four-photon resonance with the 3p2 1S two-electron state, above the ionization threshold.