A population inversion of the (001)–(100) transition in CO2gas has been observed when the cold CO2or CO2, and He gases were vertically injected into a high‐temperature, thermally equilibrated, low‐subsonic N2flow in a duct having a constant area. Simultaneously, the formation of a gas throat was observed. A small signal gain of 0.95/m was measured at 2 mm downstream from a gas injecting point.