Experimental investigation of flow in nozzles of gas-dynamic lasers

Abstract

To produce an active medium in a gas-dynamic laser, it is necessary to ensure rapid and deep cooling of a mixture of gases (usually CO2-N2-H2O). For this, one uses, as a rule, flat supersonic nozzles with a corner point that are designed for obtaining a flow with Mach number M=4.5–6. The requirements on their dimensions and profile are determined by the kinetics of the relaxation processes in the expanding gas stream and the need to obtain at the exit a sufficiently uniform field of the gas-dynamic parameters. Because of the complexity of making nozzles, one frequently uses simplified shapes, which generate shock waves in the resonator cavity. This increases the divergence of the laser beam and reduces the population inversion of the vibrational levels of the CO2 molecule [1] because of the growth of the temperature and the density behind shock waves. Therefore, for the correct interpretation of the results of measurements of the gain α of a weak signal and correct comparison with calculations, it is necessary to make a combined study of the inversion properties of the flow and the aerodynamics of the flow. In the present work, we have investigated the flow structure in a number of small flat nozzles. Data on measurements of α in a gas-dynamic laser using these nozzles are given in [2].