Optical modulation by a traveling surface acoustic wave and a holographic reference grating

The interaction of an optical beam with a traveling surface wave and a stationary holographic reference grating is studied theoretically and experimentally. The spatial phase modulation produced by the traveling wave results in an intensity modulation in the diffracted orders of the optical beam. The intensity modulation is at the fundamental frequency of the traveling wave, and its amplitude depends periodically on the separation distance between the plane of the traveling wave and the plane of the stationary holographic reference grating. Experiments were carried out with 87-MHz surface acoustic waves traveling on a LiNbO3 substrate separated from a holographic reference grating in film. The amplitudes of the detected modulation in the m = 0 and m = ±1 diffraction orders of a probing beam are in close agreement with a plane-wave analysis in the Raman–Nath diffraction regime.