Abstract

Single-mode infrared diode lasers produce high output powers with long lifetimes, ¹,² and nonlinear optical processes can be used to convert the output of these sources to the blue. For instance, 430–nm light can be generated by frequency doubling the output from a GaAlAs diode laser in potassium niobate. To increase the efficiency of blue generation, an external enhancement resonator can be used to increase the fundamental intensity inside the nonlinear crystal.³–⁸ For stable operation of such a system, a match of the output frequency of the diode laser and a resonant frequency of the external cavity must be maintained, since frequency differences will result in substantial fluctuations of the infrared power inside the resonator and thus in the blue output Passive optical feedback has been used to lock the diode laser frequency to a resonator frequency,³ with the requirement that the phase of the optical feedback be electronically controlled.⁷ As an alternative, we have used an electronic feedback technique to frequency lock the diode laser frequency to a resonator frequency to produce 54 mW of stable blue output.⁸

© 1992 Optical Society of America