Inner-shell ionization in strong high-frequency laser fields and formation of "hollow-ions"

Becker A, Faisal F. Inner-shell ionization in strong high-frequency laser fields and formation of "hollow-ions". LASER PHYSICS. 2003;13(4):430-434.Inner-shell ionization of atoms in strong laser fields at high frequencies is investigated using a simple model formula relating intense-field N-photon ionization rates to those for weak-field one-photon ionization. The probabilities Of a two-photon inner-shell ionization and the formation of a "hollow ion" are found to be most likely when the valence electron is weakly bound and the difference between the binding energies of the electron in the valence shell and the inner shell(s) is large, as for alkali atoms. A possible formation of hollow ions of the K atom is found to be very likely; it might be evidenced by detecting the subsequent fluorescence radiation due to the decay of an outer-shell electron into the inner-shell hole