The experimental and numerical studies for the effect of expansion length of supersonic nozzle for a combustion-driven CO2 gasdynamic laser facility on the small-signal gain characteristics are presented. Two types of nozzle of Circular-Circular (C-C) and Shock Free (SF) with area ratio of 20 which are able to realize Mach number of 4.7 with vibrationally nonequilibrium flow are used. For C-C nozzle at expansion length of 30mm, maximum value of the smallsignal gain coefficient is measured as 0.5m-1, and also for SF nozzle at expansion length of 45, 30 and 20mm they are 0.2 to 0.3m-1. It is shown that the higher small-signal gain coefficient is obtained at shorter nozzle expansion length, which suggests generation of a laser output extraction over the threshold value.
