Double ionization of a two-electron system in the time-dependent extended Hartree-Fock approximation

The dynamics of a two-electron system in a strong laser pulse is described by the time-dependent extended Hartree-Fock (TDEHF) scheme. Ionization yields for a one-dimensional helium model are calculated and compared with results of exact calculations (full correlation) and time-dependent Hartree-Fock calculations (no correlation). The knee structure in the double-ionization curve appears also for the TDEHF calculations, but the yields are more than an order of magnitude too low. The total ionization probability agrees well with the exact results, and much improved results for the single-ionization yields are obtained. Due to the reduced dimensionality of the model, the TDEHF ground state consists of a left and right orbital. While one of the orbitals easily transforms into a continuum state, the other remains localized and screens the nucleus, In this manner, even the one-dimensional orbitals can be considered to be inner and outer orbitals.