Mg in electromagnetic fields: Theoretical partial multiphoton cross sections

Abstract

We present ab initio calculations of multiphoton ionization cross sections---up to four---in atomic magnesium. We have followed a configuration interaction approach with the basis set constructed in terms of ${\mathrm{L}}^{2}$ integrable B-spline polynomials. The multiphoton ionization cross sections are given for a range of photon energies where the ion is left in its ground state. For the two-photon ionization process we calculate the cross section as a function of the photon energy and compare with known theoretical results. We also provide the corresponding angular asymmetry parameters which determine the angular distribution of the ionized electron. We have extended the energy range of reported theoretical three-photon ionization cross section while we present the four-photon cross section in the region between the 3s and 3p ionization thresholds. In this region the $3{p}^{2}\phantom{\rule{0.2em}{0ex}}^{1}S$ autoionizing state is identified through the four-photon absorption process and the related four-photon Fano q parameter is obtained.