Mixtures of rare gases with metal vapors are of interest for NPLs in connection with the possibility of obtaining lasing in the visible and UV ranges, while the ultimate efficiency of such lasers can be 10-20 % because of the high energy of the laser quantum and/or the possibility of using Ar, Kr, and even Xe as the buffer gases, with low energy costs of formation of ion-electron pairs. In addition, populating of upper laser levels of ions of certain metals can occur even at the first phase of relaxation processes, directly as a result of charge-transfer and Penning reactions. This circumstance makes it possible to lower the energy losses in comparison with schemes in which the populating of laser levels is implemented through longer sequences of plasma processes.

This section briefly examines the laser mechanisms and kinetic models both of operating NPLs and of certain active media on which lasing has not yet been obtained. One can become more closely acquainted with these questions in the survey and original studies cited below. Nearly all of the theoretical studies were dedicated to the kinetics of the active media of NPLs based on the transitions of ions and atoms of group II metals on the Periodic Table. Among these studies, the first of which was monograph [1], one can distinguish a cycle of theoretical investigations by IOFAN associates (see reviews [4, 106]), dedicated to analysis and calculations of the kinetics of active media of NPLs based on the transitions of Cd, Zn, Hg, Mg, Sr, Ca, Ba and Be ions. The kinetic models took into account from 100 to 160 plasmochemical reactions. The basic results of the calculations performed for the experimental conditions of the pulsed EBR-L reactor (see Chap. 2, Sect. 2.5) are shown in Table 5.10.

Among the metal vapor NPLs, active media based on mixtures of helium with Cg, Zn, and Hg vapors have elicited the greatest interest.