Radiation reabsorption in Li-like recombination lasers

Abstract

This work refers to laser-produced plasmas in which recombination from the next higher ionization stage generates lasing radiation in the X-u.v. range, and deals with the reabsorption of resonance photons which are emitted from the lower level of a lasing transition. Resonance photons, emitted in a plasma region centered on the lasing ion and whose dimensions are given by the magnitude of the absorption coefficient at the lasing ion position, are taken into account in gain coefficient calculations. The reabsorption feeding of the lower lasing level reduces population inversions and thus the gain. Any population variation of the lower lasing level induces population variations of all the other levels of the same ion, which in turn react back on the former. The absorption coefficient is calculated assuming a Voigt profile function. The peak gain coefficients of the S 13+ (95.5 and 65.3 Å) and Al 10+ (154.7 and 105.7 Å) transitions are reduced by less than 20% when reabsorption is taken into account. A slight shift of the peak gain, with respect to time and space, is noticed when reabsorption is considered. Results for Al 10+ lines are compared to experimental results and to escape probability calculations.