Abstract: The present method relates to exciting a gas dynamic CO.sub.2 laser, especially at high stagnation temperatures above 2500.degree. K and at a combustion chamber pressure above 50 bar. A liquid fuel and a liquid oxidizer are injected into the combustion chamber at these operating parameters and the produced laser gas is caused to flow through a Laval nozzle into a resonator. The flow cross sectional area of the Laval nozzle adjacent to the resonator is at least 100 times larger than the flow cross sectional area adjacent to the nozzle neck facing the combustion chamber. The flow of the laser gas through this nozzle cools the gas to about 300.degree. K, whereby an inversion state is produced. The laser for performing this type of operation has a combustion chamber connected through the above mentioned nozzle to a resonator which in turn is connected to a diffuser.