Beamed energy coupling studies

This report describes the analytical and experimental results of a study to determine the feasibility of using molecular seeds to couple CO2 laser radiation and CO laser radiation to the working fluid, H2, of a high performance rocket thruster. The gas mixtures studied experimentally were H2/H2O, H2/D2O, and H2/NH3 at CO2 laser wavelengths. The promise of CO as an absorber of CO laser radiation was established analytically. To attain the high temperatures, 1000-6000K, desired, these mixtures were placed in a cell positioned in a diagnostic apparatus which determined the spatial variation of the mixture absorption coefficient and temperature about the axis of a hot, dense plasma sustained by focused high power CW CO2 laser radiation. The measurements on these mixtures indicated their performance as couplers to exceed expectations created by the analytical study. In addition, it was found that in the absence of plasma, the temperature of the mixtures could be raised to temperatures as high as 2000-4000K simply by absorption by the mixture of laser energy at the high power beam focal spot to create the observed laser sustained flame. Further work is needed to determine the conditions under which this flame can be sustained in the laser energized rocket thruster.