A CW 10.6 μm CO2 laser has been used to measure the small-signal gain as a function of time in transversely excited capacitive discharges in CO2–He–N2 mixtures at pressures up to 1 atm. The gain of the amplifier and the average gain coefficient were measured. Different gas mixtures were investigated and the general effect of N2 and He on the gain was observed. The gain invariably increased with reduction of pressure and amplifications of greater than six were measured in an amplifier length of 2.45 m. The gain increased with the voltage applied to the discharge condenser. Deflection of the laser beam by the discharge and the production of acoustic waves in the gas were attributed to gas heating.