Diagnostics of the active medium of a homogeneous CO2 gasdynamic laser by the 'laser spectrograph' method

Abstract

The gains were measured for the lines in the traditional bands 0001–1000 and 0001–0200, in the second 0002–1001 sequence band, and in the hot band 0111–1110 emitted by the active medium of a quasi-cw homogeneous CO2 gasdynamic laser. The experimental results were fitted to a generalised theoretical model to find the translational and vibrational temperatures, and the concentration of the active molecules. It was found that, under the conditions in the active medium in the homogeneous gasdynamic laser, the use of water vapour (fraction of H2O approximately 2%) as a relaxant gas resulted in fast VT relaxation and the translational temperature was equal (with the limits of a 3% error) to the vibrational temperature T2 of the deformation mode. Under the same conditions the Fermi resonance between the 1000 and 0200 levels did not ensure the Boltzmann distribution of the populations of these levels, so that the vibrational temperature of the symmetric mode T1 was higher than T2 and the difference between them increased to 0.5 T2 when the initial pressure was reduced. Dissociation of the CO2 molecules was not detected in the active medium of the homogeneous gasdynamic laser (the proportion of CO2 was 0.11 ± 0.01, which agreed — within the limits of an error not exceeding 10% — with the value deduced from thermodynamic calculation).