SUPERSONIC CO LASER WITH RF EXCITATION

A supersonic CO laser with a maximum output power of 990 W has been developed. The gas is excited in a dielectrically stabilized radio-frequency discharge before it is cooled to a temperature of 90 K by the adiabatic expansion in a supersonic nozzle. After extraction of laser power the gas is recompressed by a supersonic diffuser and a Roots-pump system. No liquid nitrogen is needed for the operation of the laser. At a pressure of 500 mbar the rf discharge could be operated homogeneously with a specific input power of 180 W/cm3. It could be shown that the length of the discharge region and the distance between the discharge and the supersonic nozzle should be rather short. By this the vibrational relaxation of the carbon monoxide is reduced and more laser power can be obtained. The laser power can be increased by using a folded resonator system. If the laser is operated at a low Fresnel number by inserting an aperture inside the cavity, a nearly diffraction limited beam quality can be obtained. Using a supersonic nozzle with a low Mach number enables the operation of the diffuser with a high pressure recovery. Thereby the overall system efficiency is increased.