Three-photon above-threshold ionization of magnesium

Abstract

Three-photon ionization cross sections from the ground state, and two-photon ionization from the $3{}^{1}P(3s3p)$ state have been calculated for Mg in the region between the $3p$ and $4s$ ionization thresholds. These processes include an above-threshold ionization process for the last absorbed photon. We have used the Green's-function method in the Feshbach formalism and an ${L}^{2}$ close coupling approach, with a basis of ${L}^{2}$ integrable B-spline functions. We report the positions, widths, and assignments of a number of relevant ${}^{1}{P}^{o}$ ${\mathrm{and}}^{1}{F}^{o}$ doubly excited Feshbach states. We also observe unusually high cross sections due to a bound-bound transition from the $3{}^{1}{S(3s}^{2})$ to the $3{}^{1}P(3s3p)$ state, a core excitation process, and the population of an intermediate doubly excited state. Both total cross sections and angular distributions are reported.