Abstract: A laser cavity 15 is continuously flown through by a gas such as metastable iodine and other reactants, but continuous wave lasing is inhibited, except for brief periods to obtain pulsating emission of radiation; the optical energy content of the gas in the cavity 15 is, thus, depleted, and fresh gas flows into the cavity 15 during the pause following each pulse.

Abstract: The lasing action in an unstable optical resonator is controlled as to frequency by limiting frequency selectivity to an axis-near beam. The control is provided preferably outside the cavity by means of active or passive elements. A passive element returns a frequency-controlled beam into the cavity, an active element injects a control beam at the desired frequency.

Abstract: A primary nozzle provides a two-dimensionally expanding source flow of an oxidizer; a line serving as origin; and curved secondary nozzles are positioned in the primary, supersonic flow, for discharging fuel in radial direction, parallel to the oxidizer flow, mixing therewith in the laser cavity. The secondary nozzles have concavely curved, leading edges as well as concavely curved expansion edges downstream from the leading edges, positioned to cancel shockwaves from the leading edges of the respective adjacent secondary nozzles. The secondary nozzle structure provides a radially expanding fuel flow and maintains the radially expanding primary flows shock free. This radially expanding, primary flow accommodates the unused heat of reaction so that pressure is maintained nearly constant in the laser cavity. Supersonic expansion provides a low, initial pressure, and the radially expanding flow thereby maintains this pressure low.