Experimental investigation of the efficiency of overtone generation in a cw supersonic chemical HF laser

An experimental investigation was made of the feasibility of increasing the output radiation power in the generation of overtone oscillations in a cw supersonic HF laser with a radial-expansion nozzle array, which produced an active medium 70 cm long. The requirements in respect of the resonator optics were formulated. It was necessary to develop and deposit special discriminating dielectric coatings, which made it possible to achieve overtone lasing in a four-mirror cavity resonator. The output radiation power (at one-third of the nozzle array height) was about 0.5 kW at the wavelength of 1.3 μm. The corresponding overtone lasing efficiency was 6.5%. The use of resonator optics of size sufficient to collect radiation from the full height of the nozzle array should increase the output power to 1.5 kW.