We present a detailed analysis of the creation of population inversion and coherent UV radiation with a new scheme, i.e., nonlinear excitation of an inner atomic electron in a strong laser field, accompanied by filling the resulting inner-shell vacancy with an external-shell electron. Our analysis is given for the experimental results obtained by Boyer et al. in 1984 [J. Opt. Soc. Am. B 1, 3 (1984)]. The principal new features of the scheme under consideration are the following: (1) the two-electron character of atomic excitation with subsequent emission of a high-energy photon, (2) the initial absence of multiphoton resonance between the ground state and the level to be excited, and (3) strong-field-induced level crossing and excitation of the upper working level by means of Landau—Zener-type transitions.
© 1990 Optical Society of America
M. Yu. Ivanov and M. G. Malakhov, "Population inversion by nonlinear excitation of atomic inner shells," J. Opt. Soc. Am. B 7, 467-471 (1990)