Acoustic beam pattern for a push-pull laser interferometric sound sensor

Abstract

A push-pull laser interferometric sound sensor uses two parallel laser beams where both beams are exposed to the sound filled fluid. In arrays of conventional piezoelectric hydrophones, each array element produces a voltage and the beam pattern is obtained by deriving the response as a function of acoustic wave angle in terms of electrical power divided by the maximum response power along the acoustic axis. In a push-pull laser interferometric sound sensor the response function is an optical path difference or phase difference between the two laser beams as a function of acoustic wave angle. In an analogous way, we derive a response function in terms of the optical path difference between two optical line sensors as a function of acoustic wave angle and divide by the response along the acoustic axis. This normalized response function is squared to obtain the beam pattern for a push-pull laser interferometric sensor. We compare this beam pattern to that of a conventional line array.