The photoacoustic effect generated by an isotropic solid sphere

Abstract

In this paper the production of acoustic waves by irradiation of an optically thin, isotropic solid sphere is discussed. Solutions to the wave equation for the displacement potential are obtained which, together with the conservation equations for acoustic waves at an interface, give a frequency domain solution for the photoacoustic pressure. The time domain response of the sphere to a delta function heating pulse is obtained by Fourier transformation of the frequency domain expression. The photoacoustic waveform generated by a short radiation pulse is shown to depend on the radius of the sphere, the density and longitudinal sound speed of the sphere relative to those of the surrounding fluid, and the ratio of the transverse to longitudinal sound speed of the solid. Experiments are reported where a Q-switched laser was used to excite single spheres.