Directed jetting from collapsing cavities exposed to focused ultrasound

We demonstrate directed jetting from pulsed laser-induced cavities subjected to a burst of focused ultrasound. Alignment of the ultrasound focus and the pressure amplitudes in the vicinity of the cavity dictate the direction and length of the resulting jet, respectively. We interpret our observations in terms of radiation forces exerted on the cavity, due to the pressure gradient introduced to the ultrasound focus by its presence. We support our hypothesis with a linear analysis of the force distribution across the cavity surface, at the moment of maximum inflation, which shows reasonable predictive agreement with the observed jet characteristics. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3676414]