Approximate theory of multipass amplification and its application in analytic description of spectral characteristics of amplified radiation

An approximate theory of a multipass amplifier with an arbitrary degree of overlap of the amplified beams is used to consider the case of pulses with a low degree of temporal coherence. An analytic description is proposed for the energy and spectral characteristics of the radiation amplified under different conditions. It is shown that the relationships obtained can be used to describe the emission spectrum of an oscillator with instantaneous Q switching.