ABSTRACT
The most common and successful laboratory applications of the photoacoustic effect have been as analytical methods for trace gas analysis and spectroscopic investigation of solid surfaces. The physics of photoacoustic wave generation has much in common with the theory of Mie scattering: solutions to both problems require selection of appropriate wave functions and satisfaction of boundary conditions at the perimeters of the irradiated objects. It can be seen that the long pulse response of bodies having symmetry in one, two, and three dimensions is proportional to the zeroth, one-half, and first temporal derivative of the intensity, evaluated at the retarded time from the center of the radiating bodies. The uniform expansion of the body, which is the mechanical motion that launches the radiation, is monopole radiation. The analogous emission of electromagnetic monopole radiation would require the rapid creation of unipolar charge in a body, which appears to be at least difficult, if not impossible to produce.
