Probing electron dynamics in the double photoionization process of two-valence electron systems with extreme UV and soft X-ray free-electron laser pulses

We numerically investigate the removal of the two outer electrons in the X = He, Li+, C4+, Be, B+ and Ne6+ targets by the absorption of a single photon of energy in the extreme UV/soft X-ray spectral region. Our theoretical method to describe the behavior of the electrons in the presence of the laser field is based on a spectral approach of configuration interaction type to solve the time-dependent Schrödinger equation. The probe of the electron dynamics in the different systems shows that the way the outer electrons will leave their parent X system is systematically dictated by the amount of excess photon energy available to them relative to the ionization potential of the corresponding X+ ion.