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Analytical expressions are obtained for energy and angular distributions of ejected electrons at the barrier-suppression and tunneling ionization of complex atoms and atomic ions by low-frequency strong electromagnetic radiation. The results reduce to previously known expressions in the case of the ground state of the hydrogen atom. Both linear and circular polarizations of the electromagnetic field are considered. The ionization rates are found by integration over angles and energies of the ejected electron in the case of barrier-suppression ionization of complex atoms and atomic ions. The barrier-suppression results reduce correctly to the tunneling results of the Ammosov–Delone–Krainov approach in the limit of weak fields compared with the barrier-suppression fields.
В. П. Крайнов (Sat,) studied this question.