Experimental studies on the gain coefficient of an after-mixing-type CO2 gasdynamic laser are described over a wide range of various parameters. The population inversion could be generated by mixing (CO2+He) into a supersonic N2 flow, which is cooled by rapid expansion through a Lavel nozzle. The gain coefficient was found to depend on the distance from the mixing holes, and the flow rate of (CO2+He). With the increase of (CO2+He) flow rate, the gain coefficient increased linearly, and the distance from the holes for maximum gain coefficient decreased. The region where the gain was observed to be positive extended about 30cm along the flow axis, and the maximum gain was 0.8m-1 at 111mm downstream from the holes. An analysis of the gain coefficient was conducted from the measurement of the pressure and the flow speed along the flow axis.
