The bi-directional amplifier in the constant intensity approximation and its application to KrF lasers

Bi-directional and folded laser amplifiers are analysed in the constant intensity approximation. Simple analytical expressions are developed for gain, output intensity and extraction efficiency. The analysis is applied to electron-beam pumped KrF lasers and expressions for saturation intensity, small-signal gain coefficient and intrinsic efficiency in terms of gas composition and pump power per unit volume are given. The problem of fluorine burn-up in KrF lasers is discussed. Under certain conditions the analysis is shown to be equally applicable to oscillators and comparison is made with previous experimental results and computer code predictions.