Resonant parametric frequency conversion in active media

An investigation is made of the influence of saturation of the populations on the dynamics of the parametric four-wave interaction in an active medium which amplifies one of the interacting waves. Dependences of the conversion coefficient of long ($\tau_p\gg T_1$) and short ($T_2\ll\tau_p\ll T_1$) pulses on the length of the interaction zone are derived for the case of complete phase matching and in the absence of such matching. Equalization of the populations of the active levels results in breakdown of phase locking at the trailing edge of an output pulse and in saturation of the conversion coefficient. An estimate is obtained of the effectiveness of frequency addition in the case of the active medium of an HF laser. It is shown that the proposed method can be used for visualization and detection of weak laser radiation.