Influence of the oxidiser gas composition on the overtone generation efficiency of a supersonic cw chemical HF laser

An experimental investigation was made of the influence of the chemical composition of the oxidiser gas in an atomic-fluorine generator on the efficiency of generation of radiation representing the first overtone of the HF molecule in a self-contained supersonic cw chemical HF laser with the active medium 70 cm long. The optimal chemical composition was different for the fundamental and overtone transitions. A specific output energy of 84 J g-1 at a specific mass flow rate of 0.13 g s-1 cm-2 through the nozzle array was achieved by optimisation of a linear three-mirror optical cavity at the 1.33 — 1.35 μm wavelengths. The overtone radiation power generated in the whole of the active medium was 7.5 kW, corresponding to a 41% efficiency of energy conversion to an overtone.