Grating Enhanced Detection of Surface Acoustic Waves Using an Acousto-optic Modulator

Abstract

The sensitivity for enhanced detection of surface acoustic waves (SAW) using a traveling Bragg regime grating was found to be similar to that obtained using stationary reference gratings operating in the Raman-Nath diffraction regimes.1 An acousto-optic modulator (AOM) with a nominal frequency of 40 MHz was used to detect traveling gratings produced by SAW on a LiNbO3 substrate. The center frequency of the SAW was 34.88 MHz corresponding to a wavelength, ΛS, of 100 µm. With the AOM tuned to 38.5 MHz, the wavelength of the bulk acoustic wave, ΛB, in the flint glass modulator was also about 100 µm. The AOM was operating in the Bragg diffraction regime (Q'≈11) and the SAW in these experiments was a weakly modulated traveling grating, either cw or pulsed, operating in the Raman-Nath diffraction regime.2