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

The amplitude and phase of the acoustic wave radiated by an infinitely wide, optically thin fluid layer irradiated by a sinusoidally modulated light beam can be found as a solution to the wave equation for pressure. Fourier transformation of the frequency domain expression for the photoacoustic pressure gives the response of the layer to short pulse optical excitation of the layer. Solutions for plane photoacoustic waves generated by an optically thin, isotropic solid layer are given as well. An expression is derived for the far-field photoacoustic wave amplitude emitted by a fluid layer irradiated by a finite diameter laser beam. Experimental photoacoustic waveforms are given for pulsed laser and modulated, continuous wave laser irradiation of several layers.