PHOTOACOUSTIC WAVES GENERATED BY ABSORPTION OF LASER-RADIATION IN OPTICALLY THIN CYLINDERS

The properties of photoacoustic waves radiated by an optically thin, i nfinitely long fluid cylinder can be found through solution of the wav e equation for pressure. The amplitude and phase of the acoustic wave emitted by a cylinder irradiated by sinusoidally modulated light are f irst determined. The response of the cylinder to a pulse of radiation whose duration is short compared with the transit time of sound across the cylinder is then found by Fourier transformation of the frequency domain solution. The expressions derived here for the photoacoustic p ressure are shown to give the radial eigenfrequencies of the cylinder, the frequency of oscillation of a cylindrical bubble, and a response of the cylinder to long light pulses proportional to the 1/2th time de rivative of the optical pulse. The character of the photoacoustic wave s is shown to be determined, in part, by repeated reflections of the o utgoing cylindrical wave at the interface between the cylinder and its surrounding fluid. The results of several experiments with pulsed las er excitation of fluid cylinders are reported.