Transient intracavity second harmonic generation in lasers with nonlinear active media

A theoretical investigation is made of giant pulse generation in lasers with nonlinear active media which combine the functions of laser action and nonlinear optical frequency conversion, under conditions of passive and active Q switching of the laser resonator. A transversely homogeneous approximation is used to formulate the kinetic equations which describe the laser action and which are obtained by averaging, over the resonator length, the equations for plane quasimonochromatic waves traveling in opposite directions along the resonator axis. By analyzing the numerical solutions of the kinetic equations obtained assuming that the resonator is nontransmitting at the stimulated emission frequency ω₁ and that one of its mirrors is partially transmitting at the frequencies ω₂ = 2ω₁, it is possible to identify the characteristic dependences of the laser action relating to the profile, duration, peak intensity, and energy of the giant pulses and their dependence on the effective nonlinearity. It is shown, in particular, that there is an optimal value at which the laser action is most efficient. In the case of passive Q switching, there is also a limiting value of the nonlinearity above which giant pulse generation ceases completely. Possible methods of suppressing excessively high nonlinearity are briefly discussed.