Acousto-optic holography.

Abstract

Acousto-optic sensing is based on the interaction between sound and light: pressure waves induce density variations, which, in turn, alter the way light propagates in air. Pressure fields are, thus, characterized by measuring changes in light propagation induced by pressure waves. Although acousto-optic sensing provides a way of acquiring acoustic information noninvasively, its widespread application has been hindered by the use of reconstruction methods ill-suited for representing acoustic fields. In this study, an acousto-optic holography method is proposed in which the sound pressure in the near field of a source is captured via acousto-optic sensing. The acousto-optic measurements are expanded into propagating and evanescent waves, as in near-field acoustic holography, making it possible to completely characterize the radiated field noninvasively. An algebraic formulation of the wave expansion enables the use of arbitrary sets of projections. The proposed method is demonstrated experimentally by capturing the acoustic field radiated by a vibrating plate. Accurate holographic reconstructions of the pressure, particle velocity, and intensity fields are obtained using purely optical data. These results are particularly significant for the study of sound fields at mid and high frequencies, where using conventional transducers could perturb the measured field and spatial sampling requirements are challenging.