As regards the most important parameters of coherent radiation, the solid-state lasers occupy the leading positions in quantum electronics. The solid-state lasers on activated crystals and glass are used most widely in practice in different scientific and technical applications, regardless of the strong competition by lasers of other types [1].

The fundamental physical factor, determining the possibility of lasing, is the effect of induced emission of atoms under the effect of the external electromagnetic field, predicted by Einstein [2]. After the discovery of powerful sources of monochromatic electromagnetic fields in the radio-range of the spectrum, Raby examined the central problem of the interaction of laser radiation with the two-level atoms without taking relaxation processes into account and explained the main special features of its dynamic evolution [3,4].

These investigations were continued by Autler and Townes [5] who introduced the concept of the splitting of the levels of the atom, interacting with coherent radiation, i.e. the dynamic Stark effect. The special features of the kinetics of forced transitions, closely associated with the monochromatic nature of the strong external electromagnetic field, consist of the oscillation of the probability of the atom being in the combined states with the frequency proportional to the amplitude of the field. The processes of relaxation disrupt the strict dynamic nature of evolution, but the latter retain its nonlinear-dynamic nature and is controlled by the parameters of radiation [6].

The problems of formation of the inverse population of the levels were of principal importance for the development of...