EXPERIMENTAL-STUDY OF CONTINUOUS WAVE HYDROGEN-FLUORIDE CHEMICAL-LASER OVERTONE PERFORMANCE

The overtone lasing performance of the supersonic continuous wave hydr ogen-fluoride chemical laser at the University of Illinois at Urbana-C hampaign was optimized by the same set of flow rates that optimized th e fundamental performance. When the absorption/scattering losses of th e mirrors were taken into account, an overtone efficiency (the ratio o f overtone power to maximum fundamental power for the same flow condit ions) of 70-90% was achieved. The overtone efficiency was a strong fun ction of medium saturation. There was no significant change in overton e power and efficiency as the mode volume increased. However, there wa s an increase in the number of lasing lines and a shift to higher rota tional (J) lines. Overtone performance was as sensitive to cavity pres sure as fundamental performance was. There was no significant change i n overtone efficiency when the method of helium injection was changed.