Compact source of coherent blue light

Generation of 22 mW of narrow-band radiation near 430 nm was achieved by frequency doubling the 100-mW output of a single-mode GaAlAs diode laser near 860 nm. A monolithic potassium niobate ring resonator serves as the nonlinear medium and at the same time as a reference cavity for the diode-laser frequency, which optically self-locks to a cavity resonance frequency. Continuous scans of the second-harmonic frequency over 330 MHz are achieved with the electro-optic effect. The results demonstrate a portable, economical, and efficient source of coherent blue light.