Kinetics of the active medium of a He — Sr+ recombination laser: 2. Achievable energy characteristics

The mechanisms limiting the improvement of the energy characteristics of He — Sr⁺ recombination lasers with increasing pressure, active volume, and pulse repetition rate are analysed. It is found that the existence of optimal pressure is related to the cooling rate limitation for electrons at high pressures arising from the heating action of the trailing edge of a current pulse and that the average power saturation with increasing discharge tube diameter and pulse repetition rate occurs due to the formation of radial nonuniformity as well as due to the growth of the electron temperature in the afterglow. Calculations involving a mathematical model showed that the attainable maximum of the linear power is equal to ~6.2 W m^-1 for self-heating active elements of BeO ceramics and to ~7.8 W m^-1 with its surface blackened, to ~7.7 W m^-1 for an independent introduction of the vapour and to ~9.4 W m^-1 in combination with blackening, to ~17 W m^-1 for intense forced cooling of the active elements of cylindrical geometry and to ~29 W m^-1 with active elements of rectangular cross section for a wall dimension ratio of 1:3. We demonstrate the feasibility of raising the output power by ~21% in the excitation of the active medium by pulse bursts with a short interpulse separation.