Thermal self-action of acoustic wave packets in a liquid

A review is given of theoretical and experimental investigations of the propagation of powerful ultrasonic beams in high-viscosity liquids. Calculations are reported of the conditions for the observation of spatial and temporal self-compression of a wave packet as a result of sound-induced heating of a liquid. An account is given of theoretical predictions and of quantitative agreement of these predictions with experimental results on the effects of self-focusing of ultrasonic beams and of sound-induced transparency of viscous liquids. More than tenfold increase in the peak intensity of an ultrasonic pulse in the focal region, of dimensions of the order of three or four wavelengths, has been achieved under optimal conditions. Physical and biological applications of the observed effects of controlled self-action of ultrasonic waves in the bulk of a viscous liquid are discussed.