Optical detection of surface acoustic waves using stationary holographic reference gratings

Abstract

Experiments using holographically recorded phase gratings in a proximity probing method for the optical detection of surface acoustic waves (SAW) have been performed. The interaction of a probing beam with a traveling SAW and a stationary reference grating (SRG) has been analyzed and experimentally verified previously.1,2 The detected intensity in the primary orders of diffraction is modulated at the fundamental SAW frequency. For the proximity case where the SRG is separated from the SAW by a distance L, the sensitivity of detection is dependent on the separation between the SRG and SAW as well as the characteristics of the probing beam. We outline the analysis of the probing technique and present our most recent experimental results using holographic reference gratings (HRG). The SAW were produced by an interdigital transducer on a LiNbCh substrate using fifth harmonic generation. The SAW frequency was ~87 MHz corresponding to a wavelength of 40 µm. The HRG were recorded in high resolution film emulsions on glass plates. The sinusoidal periodicities of ~41 µm were measured using a Tencor Alpha-step surface profilometer. The detected intensity modulation dependence on proximity, SAW detection sensitivities, and probing laser beam effects are reported.