Abstract
We report on measurements concerning the variation of photoelectron angular distributions (PADs) from two-and four-photon ionization of ground state Mg, as the laser wavelength is scanned across the 3p(2) S-1(0) resonance. The energy dependence of the asymmetry parameters determined from the PADs and corresponding to two-photon ionization is found to be in good agreement with prior theoretical predictions. For the four-photon PADs there are at present no theoretical results. Nevertheless, the resonant character is found considerably red-shifted in accordance with earlier experimental and theoretical studies of the single and double ionization yields. In either case, the PADs show a dominant s-wave on-resonance contribution, while the d-wave contribution apparently dominates under non-resonant excitation within the scanned wavelength range. The PADs offer detailed wavelength-and channel-dependent information on the dynamics of the autoionization resonances under pulsed laser excitation, corroborating and elucidating the conclusions reached from ionization yield studies.