The gain and the saturation intensity of optimized cw 337-µm lasers are shown empirically to vary inversely as tube diameter. An expression is then derived for the power of a waveguide laser as a function of geometrical parameters, losses, and coupling. For optimized coupling the power is a strong function of tube diameter with a well defined maximum. Optimum diameter depends on tube length and losses only. The results agree well with the measured powers of three waveguide lasers delivering 30 mW, 100 mW, and 170 mW from discharges of 1-m, 2-m, and 3-m lengths. Such lasers are competitive with optically pumped submillimeter lasers.
P. Belland, D. Véron, and L. B. Whitbourn, "Scaling laws for cw 337-µm HCN waveguide lasers," Appl. Opt. 15, 3047-3053 (1976)