Bichromatic frequency conversion in potassium niobate.

Two frequency components of an IR laser beam near 980 nm are simultaneously coupled into two adjacent longitudinal modes of a passive ring resonator. A potassium niobate crystal inside the resonator converts the circulating IR light into coherent blue radiation. The total conversion efficiency is enhanced by a factor of 1.4 compared with that of conventional single-mode intracavity second-harmonic generation with the same circulating total power, and we obtain a total output power of 560 mW from 780-mW IR light incident upon the cavity. The spectra of the generated blue radiation and the circulating IR light contain a number of equidistant frequency components that are due to consecutive sum- and difference-frequency mixing.