Photoacoustic transients produced by laser generated, ultrahigh thermal gradients

Abstract

Irradiation of an absorbing surface in contact with a transparent fluid by a pulsed laser can result in generation of enormous thermal gradients. Here it is shown that the effect of such thermal gradients on photoacoustic waves is the production of fast transients that accompany the leading edge of the wave. Calculations show that the transients can be accounted for by an additional source term in the wave equation for pressure. Experiments are reported showing the predicted transients on waves from absorbing layers submerged in transparent fluids irradiated with 10 ns laser pulses.