An evaluation of mode-control and parasitic suppression in pulsed HF lasers

In this paper consideration is given to the design of unstable resonators for pulsed, high gain, HF lasers. An analysis based on geometrical mode considerations is used to evaluate the range of magnifications for which diffraction limited performance and suppression of parasitic oscillation should be achieved. The upper limit on useful resonator magnification is set by parasitic oscillation while the lower limit is defined by the mode growth-time requirements. Experiments carried out using a fast pumped, transverse discharge, HF laser equipped with plano-convex unstable resonators with magnifications varying from 1.56 - 70 are described which confirm the predicted mode control regime.