Mechanisms for the Generation and Scattering of Sound and Thermal Waves in Thermoacoustic Microscopes

Abstract

Thermoacoustic microscopes [1] generate sound by depositing energy and momentum in a solid by means of an incident laser or particle beam. These beams may be either pulsed or periodically modulated and can generate sound either through thermal expansion or by direct momentum transfer to the lattice. In general, thermal waves and both longitudinal and transverse sound waves are generated. These various waves can then scatter from thermal and elastic inhomogeneities in the solid and, by several different mechanisms, produce an acoustic signal. This acoustic signal is detected by the microscope’s acoustic transducer and used to produce an image. In this paper we describe a rigorous method for calculating the relative amplitudes of the various contributions to the acoustic signal and for assessing their importance as sources of contrast in images.