Gas lasers

A method of operating, in a pulsed mode, a transversely excited gas laser including a carbon dioxide containing lasing medium including the steps of cooling the lasing medium to a temperature such that the thermal population of the lower energy level of an output lasing transition between an upper energy level and a lower energy level of the carbon dioxide molecule is reduced, and, in each pulse, initially exciting the lasing medium to create the population inversion which results in the lasing transition at a rate which is slow enough to ensure that significant thermal population of the lower energy level is avoided during the initial excitation of the lasing medium, the lasing medium being at a pressure such that the product .alpha..sub.o C.tau. exceeds a value of approximately 30 where .alpha..sub.o is the small signal gain per centimeter length of the optical length of the laser, C is the velocity of light, and .tau. is the lifetime of the transient population immersion which results in the lasing transition.