Enhanced x-ray gain through photodepopulation

Radiation trapping currently creates one of the major limitations on population inversion, gain, and size in x-ray lasers. The resulting increase in lower-level population may be reduced by photodepletion to higher energy levels. A natural energy match between hydrogenic lasing ions of nuclear charge Z, for n=2 to 4 or 6 excitation, and Z/2 radiating ions provides a scalable system for even-Z elements.