Optoacoustic conversion in suspensions: The competition of mechanisms and statistical characteristics

Optoacoustic conversion in diluted suspensions under the effect of nanosecond laser pulses is considered. The mode of operation with moderate values of the laser fluence is studied theoretically and experimentally. In this mode, a competition of the thermooptical and cavitation mechanisms of sound conversion is observed, which leads to considerable fluctuations of the acoustic response from one laser pulse to another. Analytical expressions for the basic characteristics of the acoustic signal are obtained. A simulation of the statistical characteristics of the cavitation contribution to the signal is performed using the Monte Carlo method. The experiment is based on the use of second harmonic pulses of a YAG laser and test suspensions. The histograms of the amplitudes of acoustic signals can be used to discriminate between the mechanisms of optoacoustic conversion and also can serve as the basis for diagnosing a low content of an insoluble phase in a liquid.