Tomographic Evaluation of Sound Fields from Acousto-Optic Data

Abstract

The principles of computerized transverse tomography can be applied to the acousto-optic reconstruction of the local sound pressure of an ultrasonic field. For sufficiently narrow beams of ultrasound in the low megahertz region, the total optical phase retardation of an interrogating light beam can be considered as a projection of the sound field pressure. (Fourier techniques for the numerical reconstruction of the pressure field yield as intermediate steps a Fourier domain associated with the angular spectrum of plane waves comprising the sound field.) Consequently the sound field can be reconstructed in other regions than the plane of interrogation. In this work we discuss two alternative methods for acquiring data. One method builds the Fourier domain along radial spokes which is inconvenient for numerical processing by DFFT algorithms. The other procedure builds the Fourier domain in a nearly rectangular format compatible with two-dimensional DFFT algorithms. With this latter method, it is possible to evaluate the pressure along a line with limited data and a one-dimensional DFFT.

Work supported in part by Physical Acoustics Center Program at the Naval Research Laboratory, Code 5130, Washington, D.C. 20375.