1. lasers, the pres- second generation technology (lower h*, ence of H2o or He is extremely beneficial higher T0, Po and Ae/A*). This is clearly for the rapid deactivation of the lower lasershown by the upper curves of Figures 1 and level; indeed, such a "catalyst" is neces- 2, which typify this newer technology. For sary for the production of high gain and Ae/A* = 50, h* = 0.3mm, and T0= 1800°K, efficient extraction of laser power. The the theoretical results shown in Figure 1 typical GDL described in Reference 2 is imply that peak gain is maximum for XH2o combustion driven, therefore H2o rather 0.025, and that this maximum is fairly than He is the meaningful catalyst for flat for XH2o from 0.01 to 0.06. Indeed, a such devices. Experience gained with the more detailed study of the theoretical first generation of GDL technology indi- results reveals that, for the stronger cated that gain is a very sensitive expansions associated with the second generfunction of H2o content; along with the ation nozzles, the lower laser level as well beneficial deactivation of the lower level, as the upper level tends to freeze inside there is also the competing detrimental the nozzle. Hence, more H2O is necessary deactivation of the upper level due to H2O. to promote rapid equilibration of the lower Hence, with the first generation of GDL's, level with the translational energy of the an optimum amount of H2o in the gas mixture gas. This effect is shown in Figure 3, was found to be on the order of 1 percent, which illustrates the variations of the i.e., XH O = 0.01.
2. The results shown in Figures 1-4 are theoretical. Are they reliable? We believe so, because our calculations based on the fully coupled time-dependent nonequilibrium nozzle analysislO, 12, 13 have yielded reasonable agreement in the past with our own experiments, as well as the data of others (see