Enhanced detection of acoustic waves using thick and thin reference gratings

Abstract

Propagating acoustic waves typically produce small effective refractive-index variations and can thus be difficult to detect by simple optical probing. It has been shown that use of stationary reference gratings can greatly facilitate the detection of these waves. In this paper, the application of thick (Bragg diffraction regime) and thin (Raman–Nath diffraction regime) sinusoidal-phase reference gratings is considered for enhanced detection of acoustic waves, and their relative performance is compared. Simple, analytical expressions are obtained that describe the diffraction characteristics in each case. It is shown that thick reference gratings produce a purely sinusoidal temporal-intensity modulation, whereas thin gratings, in general, produce nonsinusoidal modulation.