Two-, three-, and four-photon ionization of Mg in the circularly and linearly polarized laser fields: Comparative study using the Hartree-Fock and model potentials

We theoretically study multiphoton ionization of Mg in the circularly polarized (CP) as well as the linearly polarized (LP) laser fields. Specifically two-, three-, and four-photon ionization cross sections from the ground and first excited states are calculated as a function of photon energy. Calculations are performed using the frozen-core Hartree-Fock (FCHF) and also the model potential (MP) approaches and the results are compared. We find that the MP approach provides results as good as or even slightly better than those by the FCHF. We also report the relative ratios of the ionization cross sections by the CP and LP laser fields as a function of photon energy, which exhibit clear effects of electron correlations.