Influence of operational parameters on the efficiency of overtone generation in a supersonic cw chemical HF laser

An experimental investigation was made of the influence of the mass flow rate of the fuel components and of the position of the axis of an optical cavity on the efficiency of generation of radiation representing the first overtone of the HF molecule in a supersonic cw HF laser. The length of the active medium was 70 cm and a radial-expansion nozzle array was used. An output radiation power of 2.61 kW (from one third of the nozzle array height) was generated at the wavelength ~1.3 μm in a three-mirror optical cavity. This corresponded to the overtone generation efficiency of the laser amounting to ~35% and the overtone generation efficiency of ~50% when considered from the point of view of conversion of energy of the active medium. The output radiation power could be increased to ~8 kW by the use of cavity optics capable of utilising the radiation from the whole height of the nozzle array.