Abstract

We report on generation of tunable narrow bandwidth violet (420-427-nm) radiation by frequency doubling an IR diode laser in a potassium niobate (KNbO₃) crystal in an external ring resonator. The external cavity enhances the fundamental beam, thus increasing the efficiency of second harmonic generation, and also is used to narrow the linewidth of the fundamental laser. The diode laser frequency is optically stabilized to the external ring cavity resonance frequency by a new variation of the technique of Dahmani et al.¹ The optical feedback is obtained from the weakly excited counterpropagating mode in the ring cavity. With 62 mW of input power and 1160 mW of intracavity power, we have produced 6.7 mW of second harmonic power at 426 nm. The violet output beam is unidirectional and is in a TEM₀₀ Gaussian mode determined by the resonator rather than the laser diode output beam.

© 1990 Optical Society of America