Direct versus Sequential Double Ionization of Mg with Extreme-Ultraviolet Radiation

We present an ab initio calculation of multiphoton double ionization in atomic magnesium, the first of its type in an atom with a complex core, showing that direct correlated double electron ejection can be studied through analysis of the photoelectron energy spectrum, using currently or upcoming extreme-ultraviolet radiation sources.

Figure 1

Mg energy level diagram (in eV), showing the direct and sequential ionization channels.

Figure 2

Direct two-photon double ionization cross section in the range 14–17 eV.

Figure 3

Photoelectron energy spectrum for the 9th harmonic of the Ti:sapphire laser (780 nm) with a 50 fs, Gaussian pulse and peak. Intensity ${10}^{12}\mathrm{W}/\mathrm{c}{\mathrm{m}}^{\mathrm{2}}$. The flat part of the spectrum between 0 and 5.9 eV represents the probability for the direct double ejection as a function of the kinetic energy of the one of the photoelectron, at the end of the pulse, while the peaks correspond to sequential processes indicated in Fig. 1.