The overtone performance of our supersonic cw HF chemical laser, which was measured with well characterized mirrors, was used to determine the Rigrod parameters g_o and I_sat. Rigrod theory showed that higher medium saturation yields a higher overtone efficiency, but does not necessarily yield a larger measurable power. A new technique to measure the reflectivities of high-reflectivity mirrors using measured mirror transmissivities, outcoupled power, and Rigrod theory with an accuracy of ±0.07% was demonstrated. For low absorption/scattering loss mirrors, when the gain length is long enough to well saturate the medium, the intracavity flux (hence the mirror loading) can be reduced by more than a factor of two with only a 5% penalty in outcoupled power.

The SBS process requires the HF laser and amplifier to operate on only a few lines so that all of them will have the requisite power to utilize the SBS process. This requirement brings to the forefront a question that has been of interest ever since it was shown that the HF laser operated on many lines simultaneously: what fraction of the multiline performance can be achieved when a cw HF oscillator and amplifier are operated on only one or two lines? To answer this question, the line selected oscillator performance is being measured as a function of the cascade pair, the peak gain lines in each and in one vibrational band and compared with multiline performance.

To investigate the role of mixing on HF overtone laser efficiency, a new nozzle, which injects the helium and hydrogen through orifices in the side wall of the supersonic portion of the nozzle, was designed and constructed. Preliminary tests indicate that the fundamental performance of this nozzle is twice that of the parallel slit nozzle. The overtone performance is being measured and compared to that of the parallel slit nozzle.

Research is being carried out to determine the flow physics and nonequilibrium behavior of a new high-pressure chemical laser. Computational experiments include mixing speeds, chemistry states, and efficiencies of new systems.

Aeronautical and Astronautical Engineering