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

The overtone lasing performance of the supersonic continuous wave hydrogen-fluoride chemical laser at the University of Illinois at Urbana-Champaign was optimized by the same set of flow rates that optimized the fundamental performance. When the absorption/scattering losses of the mirrors were taken into account, an overtone efficiency (the ratio of overtone power to maximum fundamental power for the same flow conditions) of 70-90% was achieved. The overtone efficiency was a strong function of medium saturation. There was no significant change in overtone power and efficiency as the mode volume increased. However, there was an increase in the number of lasing lines and a shift to higher rotational (J) lines. Overtone performance was as sensitive to cavity pressure as fundamental performance was. There was no significant change in overtone efficiency when the method of helium injection was changed.