Sound field reconstruction based on the acousto-optic effect

Acoustic measurements are usually carried out with transducers that interact mechanically with the sound field under investigation. The goal of this work is to employ a completely different measurement principle, the determination of sound pressure based on the interaction between sound and light, namely the acousto-optic effect. When sound propagates through a medium, it gives rise to pressure fluctuations that change the instantaneous density of the medium. Under such circumstances, the speed of light is not constant, but changed by the acoustic field. This acousto-optic interaction can be measured with a laser Doppler vibrometer; furthermore, it can be exploited to characterize an arbitrary sound field using tomographic techniques. This paper briefly reviews the fundamental principles governing the acousto-optic effect in air, and presents an investigation of the tomographic reconstruction within the audible frequency range by means of simulations and experimental results. The good agreement observed between simulations and measurements is further confirmed with representations of the sound field obtained with traditional microphone array measurements.