Application of a single frequency unstable cavity to a CW HF laser

Demonstrations of diffraction limited performance from a CW diffusion-type HF chemical laser are reported. A novel type of edge coupled non-confocal unstable resonator consisting of a convex mirror and a diffraction grating is used. The quality of the single wavelength beam produced is found to be superior to that of a conventional edge coupled multi-frequency unstable resonator in the sense that well defined side lobes corresponding to a coherent source are observed. It is hypothesized that the difference between the single line and multiple line results is due in part to the non-uniform gain distribution of the multi-line active medium of the CW chemical laser. A new technique of coupling power out of an unstable resonator different from the edge coupling previously suggested by Siegman is also applied. This consists of coupling power out directly through the diffraction grating zero order radiation. By this technique a large fraction of the total power is concentrated within the diffraction limited main lobe--a result difficult to achieve with the conventional annular coupling method. Peak power levels of the order of 100W have been achieved on the (P2(5)) line for flow conditions yielding approximately 1 kw in closed cavity measurements.