Numerical simulation of a Q-switched cw chemical HF laser

A mathematical model of a Q-switched cw chemical laser is developed. The model is based on a simplified description of the active medium and the exact wave description of the mode structure of radiation. The model is used to study numerically the spatial–angular parameters of the output beam of a HF laser. We considered an unstable cavity that provided a high stability of the axis of the laser-pulse radiation pattern upon Q-switching with the help of a rotating mirror. The results of numerical simulation showed that for typical dimensions of a plane or an unstable cavity of the positive branch in a cw chemical laser, the angular radiation divergence rapidly changes in time and on average exceeds the diffraction limit by an order of magnitude. The problem can be solved by replacing a rotating mirror Q switch by a fixed one with time-dependent transmission. We also considered a negative-branch unstable cavity which can provide a stable radiation divergence upon Q-switching produced by a rotating mirror.