Bragg diffraction of light by two orthogonal ultrasonic waves in water

Abstract

The diffraction of a light beam by two orthogonal traveling ultrasonic waves in water under Bragg angle incidence is described. It is shown that under low index modulation, only the zero order (0, 0), the two minus one orders (−1, 0 and 0, −1), and the cross minus one order (−1, −1) predominate in the diffraction process. Equalization of the four beam intensities, which is required in a two-component cross-beam laser Doppler velocimeter system, can be achieved with the transducers being driven at low power levels.