Optical Sound Measurement

Abstract

As airborne sound is density variation, it can be measured optically by detecting the refractive index of air, enabling us to observe a sound field not tractable by a microphone. In this paper, the history and principle of the optical measurement of audible sound are presented together with the methodologies (laser Doppler vibrometry and high-speed polarized interferometry). Some examples of optically measured sound fields are also shown.