Laser-nucleated Acoustic Cavitation: Size Matters

Gerold, B., Joy, J., Prus, O., Grinfield, J., Volovyk, A., Medan, Y., Melzer, A., Cochran, S. and Prentice, P. (2011) Laser-nucleated Acoustic Cavitation: Size Matters. In: WIMRC 3rd International Cavitation Forum 2011, Warwick, United Kingdom, 04-06 Jul 2011,

Abstract

We report on the development of an instrument for hybrid ‘sonoptic’ cavitation studies. A focused ultrasound transducer is housed in a custom built chamber, which permits optical access to the focal volume, without perturbing the propagating acoustic field. This configuration allows pulsed-laser irradiation of the fluid at the focus, and simultaneous high speed observation of cavitation activity in this region. In this paper we provide a brief description of the apparatus and present preliminary data on distinct cavitation regimes we have observed. Specifically, laser-induced cavitation in an established field, and a new phenomenon that we refer to as laser-nucleated acoustic cavitation. The former involves a laser pulse of energy above the threshold value for optical breakdown for the medium, in a pre-established ultrasound field. Here, a cavity rapidly expands to a maximum diameter of a few 100µms, from the plasma generated on absorption of the optical energy, and collapses to form debris that is subsequently driven by the ultrasound radiation. By contrast, laser-nucleated acoustic cavitation is initiated by a pulse of energy below the ambient breakdown threshold, in a pre-established field. For this regime, either form of radiation does not result in cavitation activity without the other. In combination, the role of the laser pulse is to initiate activity which is dominated by the ultrasound exposure from the outset. Crucially, the spatial and temporal precision afforded to the occurrence of cavitation by laser-nucleation, allows the use of high speed micro-photography to resolve cavitation cloud evolution and behavior. This allows us to consolidate our assertion of acoustic cavitation, with close-up ultra-high speed images of the clouds, and observation of constituent cavity sizes. It is expected that such observations will contribute to a greater understanding of cavitation in focused ultrasound, including for potential future therapeutic applications.

• Item Type: Conference Proceedings
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Gerold, Dr Bjoern and Cochran, Professor Sandy and Prentice, Dr Paul
• Authors: Gerold, B., Joy, J., Prus, O., Grinfield, J., Volovyk, A., Medan, Y., Melzer, A., Cochran, S., and Prentice, P.
• College/School: College of Science and Engineering > School of Engineering; College of Science and Engineering > School of Engineering > Systems Power and Energy