Excitation mechanisms of the electron-beam-pumped atomic xenon (5d→6p) laser in Ar/Xe mixtures

Abstract

The atomic xenon laser operates on seven infrared transitions (1.73–3.51 μm) between the 5d and 6p manifolds. Intrinsic laser power efficiencies exceeding 5% have been previously obtained in Ar/Xe mixtures, principally at 1.73 μm (5d[3/2]1→6p[5/2]2). The kinetic mechanisms responsible for this performance, though, are not well understood. In this paper, we report on a computer model for the electron-beam-pumped xenon laser in Ar/Xe mixtures with which we have investigated some of these excitation mechanisms. Based on the results of a parametric study of power deposition (50 W cm−3 to 100 kW cm−3), gas pressure (0.5–6 atm), and xenon fraction, we suggest that the high efficiency obtained in Ar/Xe mixtures is due to rapid collisional cascade to the upper laser level of the 1.73-μm transition following dissociative recombination of ArXe+ and selective quenching of the lower laser level of the 1.73-μm transition by collisions with argon. The results of our model indicate that the decrease in laser performance at high Xe fractions results from electron-impact excitation of the lower laser levels (6s→6p) and quenching of the 5d manifold by collisions with atomic xenon. The degradation of laser performance at high specific power deposition is most likely due to electron-collision mixing of the 5d and 6p manifolds. As a result of the lower levels being cleared dominantly by atomic collisions, we predict that optimum performance is then obtained at higher gas pressures when increasing power deposition. The results of the model predict that optimum power deposition is obtained when the fractional ionization is ≊2–3×10−6.