Double-color-pumped photorefractive oscillator and image color conversion

Can two laser beams of different colors interact with each other to initiate a photorefractive oscillation in a slowly responding (~1 sec) crystal? We report on the operation of this new nondegenerate four-wave mixing device, in which two other beams and the gratings are efficiently self-generated. An application for image color conversion is demonstrated. In an experiment, we used for the two pumps combinations of the lines of an argon-ion laser (514.5, 496.5,488,476.5, and 457.9 nm) and a He-Ne laser (632.8 nm). The mixing crystal was BaTiO₃ with a photorefractive time constant of the order of 1 sec.