Threshold evaluations for an x-ray laser

Photoelectric pumping of inner shells of intermidiate Z materials is shown to be efficient for inverting the population of radiative transitions around 1 keV. Non-radiative processes are shown to be essential for achieving a stationary inversion. Reported intense X-ray bursts from plasmas generated by laser radiation suggest the use of a Nd laser as exciting source. Threshold evaluations show that a mirrorless X-ray laser is possible by use of nowadays available Nd lasers.