Calculation of the power characteristics of a double-pass amplifier

A two-level model of the active medium is used to analyze the characteristics of a double-pass amplifier for a phase-conjugation laser system. Attention is given to the amplification of opposite waves in the active medium with a homogeneously broadened transition line. The approximation of plane monochromatic waves is used to calculate the stationary dependences of the gain, output intensity, and efficiency of the amplifier on its parameters and the level of the input signal. It is shown that radiation losses due to absorption in the matrix of the active material or due to incomplete reflection from the mirror situated behind the amplifier lead to optimal operating modes of the amplifier which correspond to maximum values of the efficiency or output intensity.