Estimate of the stimulated emission cross section of a four-level active medium from the kinetics of decay of its superradiance

An analysis is made of the problem of kinetics of the superradiance decay in the case of nonlinear quenching of excited centers in four-level active media. A method is proposed for estimating the initial axial gain and of the stimulated emission cross sections of active media: it is based on a simultaneous analysis of the normalized superradiant flux and integrated population of the active medium. The proposed method is not sensitive to nonlinear quenching. A qualitative analysis is made of the decay of excitation in neodymium pentaphosphate crystals after pulsed excitation with laser radiation of the 0.538 micron wavelength and stimulated emission cross sections are estimated for the 4F(3/2) - 4I(1 1/2) transition in Nd(3+) resulting in lasing at 1.051 micron and at some other wavelengths of this transition.