| Popis: |
Using an exact, three-dimensional, Green's function solution to the thermoelastic equations in semi-infinite solid, we have calculated the relative generation efficiencies of thermal waves, longitudinal acoustic waves and transverse acoustic waves induced by a periodically modulated beam of light or particles. The angular distributions and strengths of energy transfer and momentum transfer contributions are compared. Scattering and mode-conversion effects are discussed. Theory "Thermoacoustic microscopes"' are devices which generate sound in solids by means of focused beams of light or particles (either electrons or ions). These beams may be either pulsed or periodically modulated and, loosely speaking, generate sound through the response of the solid to the energy and momentum they deposit in it. The detection of that sound is accomplished by means of an acoustic transducer somewhere on the surface of the solid, and the microscopic image is generated by recording the signal from the transducer as the beam is scanned over the region of interest. In this paper we present a detailed, three-dimensional theory for the generation of sound in such a microscope. The starting point for the calculation is the (linearized) set of equations2 which describe the conservation of energy and momentum in the solid |
