Generation of Acoustic Waves in Liquids by Pulsed Lasers

Abstract

The generation of acoustic transients in liquids by laser impact is described both experimentally and theoretically. The experiments were performed with a hybrid-CO2-laser whose beam was focused perpendicular onto the free surface of various liquids. Special piezoelectric transducers developed in our laboratory were used for the detection of the acoustic waves. Three different regimes could be distinguished with respect to the time dependence of the acoustic signal. One of them corresponds to the pure photoacoustic effect as the wave generating mechanism. The possibility of inducing acoustic waves with tunable high frequencies in the MHz range in this case indicates the transient character of this process. On the basis of this result a new spherical model on the photoacoustic effect is proposed in which the laser heating process is represented by the three-dimensional heat pole. Our analytical model provides excellent agreement with the experimental results.