Calculation of energy characteristics of double-passage amplifier

Amplification of the return waves in a two-level active medium with a uniformly broadened transition line is investigated. The gain, output intensity, and efficiency of a double-passage amplifier are computed as a function of the amplifier parameters and the input signal level using an approximation of planar monochromatic waves. It is shown that radiation losses caused by absorption in the matrix of the active substance, or caused by incomplete reflection from the mirror behind the amplifier, result in optimal operating modes of the double-passage amplifier which correspond to a maximum efficiency of intensity of the output radiation. Even a slight reduction in the divergence of the output radiation (by less than a factor of 2) makes it possible (by exploiting the wavefront phase conjugation effect) to create a more efficient laser system with better radiation power density per unit of solid angle.