Laser excitation of atomic inner-shells by coherent processes with implications for X-ray lasers

Experimental studies of multiphoton processes using high-brightness ultraviolet excimer laser sources are interpreted in terms of a new mechanism for producing highly excited states of atomic inner-shells. The macroscopic electric field associated with a spatially and temporally coherent intense laser pulse can be made to equal or exceed the Coulomb field experienced by the electrons in the outer-shell. The model predicts that all of the electrons in the outermost sub-shell will execute an ordered coherent motion that can couple strongly to inner-shell electrons to produce highly excited inner-shell states and vacancies. This may, in favorable cases, result in population inversions for transitions in the 100 to 1,000 eV range. The experimental basis for this mechanism, scaling estimates based on this analysis, and potential applications of this technique are presented