Photoionization of two-electron atoms has been studied theoretically by
different authors starting from pioneering
paper by Wheeler. In this
paper, authors developed the complex rotation method (CRM) for highly
accurate calculations of the
Photoionization cross-section of
two-electron
atomic targets. Here, authors use the CRM in
nonperturbative
procedure by applying it to the whole system the atom
plus the electromagnetic field. Thus, this procedure are capable of
going beyond the perturbation theory and considering very strong
fields. The formalism developed using the language of square-integrable
functions with a finite norm. This approach becomes feasible in the
so-called Floquet-Fourier representation of the time-dependent
Schrodinger equation. With the use of the Hylleraas-type basis
functions, the
total photoionization cross-sections are obtained within
the accuracy of a fraction of a percent.
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