Single- and two-photon ionization of neutral Ca

Using a combination of B-spline-based model potential techniques with R-matrix Floquet theory, we have carried out single-photon and two-photon ionization calculations of Ca. Good quantitative agreement is obtained with experiment for the single-photon ionization cross-section above the first threshold. We investigate the intensity dependence of the photoionization spectra, and also illustrate how laser-induced degenerate states affect it. Inclusion of the spatial and temporal profile of the laser pulse is examined. The two-photon ionization spectra, below the 3d(2)D(e) threshold, show a clear perturbation due to the interloping 4p(2) S-1(e) State.