Abstract

When two coherent beams of identical frequency intersect they interfere with one another, creating a stationary intensity pattern. This interference pattern will have planes of constant phase at an angle which bisects the two crossing beams. The spatial position of the intensity maxima depends upon the relative phase of the two interacting beams. When these two beams cross in a photorefractive material, photoinduced charges migrate or diffuse from high-intensity regions to low-intensity regions. The resultant spatial modulation of the charge density produces a spatially varying electric field. The electric field then produces a refractive index grating through the linear electrooptical effect. Because the electric field depends on the gradient of the electric potential, the resultant index grating is phase shifted from the interference pattern by π/2. The result of the non-local index grating is an isotropic scattering of the two incoming beams off of this grating. The net result is the coupling of energy out of one beam into the other. Provided the gain-length product for the coupling phenomenon is sufficiently large, essentially all of the energy is coupled into one beam while the other beam is extinguished. This two-wave mixing process can be understood by looking at the relative phase shift of the scattered light relative to the original laser beams.

© 1987 Optical Society of America