A second-harmonic, ring dye laser for the generation of continuous-wave, single-frequency UV radiation

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Abstract
A frequency-doubled, continuous-wave ring laser is described, capable of generating 3 mW of single-frequency UV light, with a tuning range from 292-302 nm using ADA as the doubling crystal. The crystal is Brewster-angled and incorporated into an arm of the cavity compensated for astigmatism and coma. Cavity analysis predicts the stability region, spot sizes and positions of the foci in the dye jet and crystal, and enables mode matching to be optimized. A unidirectional device, used to maintain oscillation of the laser with one direction of circulation is described. The ring configuration enables single mode operation to be maintained with only one, thin, tuning etalon in the laser cavity. Using a servo-control circuit, the laser frequency is locked to an external reference cavity to minimise long-term drift, and to enable the single mode to be scanned continuously through 6 GHz in the UV.