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

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).