Diagnostic techniques for HF/DF laser cavities

Abstract

Advanced techniques for HF/DF laser diagnostics have been developed, tested, and applied to the measurement of HF laser cavity characteristics. In this paper we shall discuss the experimental techniques, potentials, and limitations on the basis of diagnostic data which will be presented. The detailed discussion of the measurement results will be discussed in a separate paper. Diagnostic techniques to be discussed will include chemiluminescent infrared analysis of the HF fundamental band which permits a determination of flow field rotational and kinetic temperatures with very high accuracy. Excited HF vibration-rotation state number densities down to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim10^{11}</tex> excited molecule/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> can be determined from absolutely measured line intensities using 30-s spectrometer scan times. Measurements problems related to considerable cavity medium gain or absorption will be discussed in detail. Application and advantages of diagnostic chemiluminescence using harmonic HF transitions <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Delta\upsilon = 3, 4</tex> ,and 5 in the near IR and visible spectrum, detectable with photoemissive detectors, have also been considered and applied. Flow field visualization has been achieved by high speed infrared mapping and "orange glow" photography. The data presentation, interpretation, and comparison of the different flow field visualization techniques will be considered. In order to determine the important HF ground state concentrations in laser cavities we have utilized an infrared HF resonance absorption method with most encouraging results. The latter method has also been applied to the direct measurement of small-signal gain for both the 1-0 and 2-1 HF transitions. We shall further discuss the applications of laser scattering and electron beam excited fluorescence to the measuremeat of important laser cavity characteristics.