Model calculations for a 600 Å laser based on photopumping of Mo⁶⁺ by a spectral line of Mo¹¹⁺

We assess aspects of the feasibility of a recent proposal to use the coincidence between a Mo¹¹⁺, 136.499 Å, line and a 4p⁶-(4p⁵)_1/26s, J = 1, transition of Mo⁶⁺, to obtain amplified spontaneous emission around 600 Å. [Feldman and Reader, J. Opt. Soc. Am. B6, 264 (1989)]. A collisional-radiative model for the Mo⁶⁺ ion, including resonant photoexcitation of the 4p⁵_1/26s level, was constructed using the HULLAC atomic physics package. The model included the 4s²4p⁶; 4p⁵4d, 4f; 4p⁵5s, 5p, 5d; 4p⁵6s, 6p, 6d; 4s4p⁶4d, 4f; 4p⁶4d² and 4s²4p⁴4d² configurations, amounting to 193 levels. All configuration interactions and collisional mixing were taken into account. A gain of 3 cm^-1 is obtained for the 4p⁵6s(J = 1)-4p⁵5p(J = 2) transition at 645 Å with T_e = 5 eV, n_e = 10¹⁸ cm^-3, and an effective radiation temperature of T_rad > 40 eV for the pump transition. Other transitions exhibit lower gains.