LIMITING FACTORS IN PRF SCALING OF BARIUM VAPOR LASERS

We have studied the factors limiting the performance of a barium vapou r laser (BVL) as the pulse repetition frequency (PRF) is elevated. By measuring the population densities of key barium species, we have foun d that increasing the PRF leads to progressively larger depletion of t he axial pre-pulse Ba ground-state density (up to 85% at 15 Mit PRF), due to the combined effects of ion pumping and gas heating. A direct c onsequence of this Ba density depletion is a proportional decrease in the peak upper laser-level density of the 1.50 mu m and 1.13 mu m lase r transitions (i.e. (BaP1)-P-1) during the excitation pulse. The resul ts suggest that ground-state depletion is the dominant factor limiting laser output at high PRFs, and that the effects of the pre-pulse lowe r laser-level and electron densities play a secondary role. The implic ations to the PRF scaling of BVLs and other metal vapour lasers are di scussed.