Fiber optic probe hydrophone for the study of acoustic cavitation in water.

We use focused ultrasound bursts to submit a liquid to mechanical tension. When the pressure in the sound wave reaches a sufficiently low value, vapor bubbles are nucleated in the bulk liquid. According to nucleation theory, increasing the ultrasound frequency increases the cavitation threshold by a calculable amount. To check this, we have built a fiber optic probe hydrophone based on one originally proposed by Staudenraus and Eisenmenger [Ultrasonics 31, 267 (1993)]. We have adapted the pressure calibration and data analysis of this tool to make it appropriate for precise measurements of tension in liquids. We are able to resolve the fractional change in the pressure threshold for cavitation in water that results from a twofold increase in the frequency. This provides a test of nucleation theory in general.