EVOLUTION OF EXCITED AND GROUND-STATE SPECIES DURING BURST-MODE EXCITATION OF A BARIUM VAPOR LASER

We have studied the development of steady-state prepulse conditions in the barium vapor laser (BVL) and the factors that influence steady-st ate laser output using the ''hook'' method. The ground-state and excit ed-state Ba and Ba+ species were measured during the afterglow, and th e (BaP1)-P-1 upper laser level during the excitation phase, of selecte d pulses in a burst of excitation pulses at 8 kHz. Results show that l arge depletion of the prepulse (BaS0)-S-1 ground-state density from th e axial region of the tube occurs during the burst, and proportional d ecreases in the peak upper-laser-level density occur during the excita tion phase. The prepulse electron density (inferred from the total Ba density) and lower-laser-level densities do not accumulate during the burst, and it is concluded that ground-state depletion is primarily r esponsible for the decrease in laser pulse energy that occurs during a burst as reported by Pask and Piper. We observe significantly greater depletion of the ground-state density on-axis in the presence of neon buffer gas than helium, which we attribute primarily to the high ioni zation observed in neon and the corresponding increase in the effects of ambipolar diffusion. The results highlight the influence of buffer- gas composition on the establishment of steady-state prepulse conditio ns (and therefore the steady-state laser pulse characteristics). The r esults have implications to metal vapor lasers in general, including t hose operating with buffer-gas additives.