For the development of L-innershell X-ray lasers using femtosecond, high-power lasers

The development of keV X-ray lasers based on inner-shell atomic transitions requires extremely fast energy deposition on a target in order to effectively compete with the inherently fast (0.1-20 fs) atomic decay processes. The duration of ultrahigh peak power laser systems is now reaching this timescale. In principle, these systems can be used to produce sufficiently short and energetic X-rays or electrons for pumping inner-shell transitions. In this paper X-ray laser schemes in which the Coster-Kronig Auger process is the dominant lower level decay mechanism are described. Such systems have inherently short lower level lifetimes and under certain conditions can be inverted both with excitation by energetic electrons as well as X-rays. They are therefore relatively immune to secondary electron ionization and have simpler geometric considerations than previously proposed inner-shell laser schemes. For appropriately chosen atomic species and transitions, the population inversion between inner-shell hole states can be created by electron collisional ionization only - a situation which has previously been considered impossible. We have reviewed radiative and non-radiative decay rates from inner-shell vacancies in elements up to Z=90. Computer simulations show that among these transitions the L/sub 2/M/sub 1/ transition for Z=22 to 32 is the most robust to detrimental collisional processes.