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-state laser output using the “hook” method. The ground-state and excited-state Ba and Ba⁺ species were measured during the afterglow, and the Ba¹P₁ upper laser level during the excitation phase, of selected pulses in a burst of excitation pulses at 8 kHz. Results show that large depletion of the prepulse Ba¹S₀ ground-state density from the axial region of the tube occurs during the burst, and proportional decreases in the peak upper-laser-level density occur during the excitation 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 responsible for the decrease in laser pulse energy that occurs during a burst as reported by Pask and Piper (1994). 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 ionization 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 conditions (and therefore the steady-state laser pulse characteristics). The results have implications to metal vapor lasers in general, including those operating with buffer-gas additives