Continuously - excited lasers of the CO u mixing, and supersonic CO, types. There is specifically disclosed a method, and a laser apparatus, for producing a repetitively pulsed output, in which a stream of excited gas, of the type having a relatively long excitation life, is produced, stored and subsequently transferred, in the form of pulses, to a power extraction zone incorporating a resonator. In one example the gas laser is a supersonic CO laser in which the CO is excited in the excitation zone and is, after storage, transferred under supersonic conditions to the resonator. In the main example the gas to be excited is N u which is initially transferred to a storage chamber provided between a rotatable storage cylinder (16) and an axial supporting shaft (18) therefore, and thereafter the N u is transferred through holes (17) in the storage cylinder (16) which align during rotation with slots (20) through a surrounding fixed cylinder (19) to allow pulses of excited gas to be transferred to the power extraction zone (12) where it is mixed with CO u and He, entering through supply tubes (23), and to which it transfers its excitation before flowing to the resonator.