Effect of the shape of the supersonic part of the nozzle on the redistribution rate of molecules by vibration levels in the active medium of CO gasdynamic lasers

The vibrational relaxation behavior of CO molecules in supersonic flows of various expansion geometries has been investigated theoretically with a view to optimizing the profile of the nozzle second stage. It is shown that in mixtures with low inert gas content, and in particular in pure CO, the maximum optical gain coefficient increases monotonically with decreasing temperature of the active medium due to increased expansion ratio of the gas flow. However, because of a decrease in the V-V exchange rates at lower densities and temperatures, an increase in the expansion ratio may result in a lower gain coefficient. In order to maximize the optical gain coefficient at high CO contents, the profile of the nozzle supersonic stage should be selected with allowance for the kinetics of CO molecule redistribution by vibration levels.