Optoacoustic analysis of the laser-cleaning process

Laser cleaning is an optodynamic process in which the optically induced removal of a liquid or a solid contaminant from a substrate is accompanied by a optoacoustic wave in the surrounding air. In our experiments we used both dry and steam laser-cleaning techniques for various samples. Optoacoustic wave, produced by the abrupt heating and detachment of the contaminants, was observed with a probe-beam deflection technique. We determined two characteristic parameters of the optoacoustic wave: the amplitude and the time-of-flight of the acoustic signal. With an analysis of these waves we also determined possible generating mechanisms. The decrease of the amplitude and the velocity of propagation, which approaches sonic speed, of the consecutive waves indicate that the dynamics during the laser-cleaning process is progressively weakened. The cleaning process is over when both the parameters reach a constant value, so with measuring optoacoustic waves the progress of the cleaning process could be observed on-line.