Schematic overview of apparatus, including BNC trigger lines and ultrasound electronics.
Representation of the custom-made sonoptic chamber, constructed according to the dimensions of the focused ultrasound field. The Shimadzu HPV-1 high-speed camera is depicted. Inset top right is the Schlieren imaging arrangement for alignment of the ultrasonic and optical foci. Inset bottom right is a close up of the cavitation chamber which contains the ultrasound (blue) and laser (green) foci.
(a) Scanned axial and transverse pressure fields of the focused bowl transducer used as the ultrasound source throughout the experiments, recorded in an ultrasound scanning tank. (b) Simulation of field based on the dimensions of the transducer.
Cubic interpolation of the two-dimensional scans, with sample pressure data measured in the acoustic focus within the sonoptic chamber (black dots), demonstrating ultrasound propagation.
(a) Schlieren image of cavitation chamber, used to align the laser focus (green spot) to that of the ultrasound (lighter blue region). The omnidirectional needle hydrophone used to record acoustical emissions during cavitation activity is also visible. (b) Fourier spectra of sound field where (i) MI = 0.6 and (ii) MI = 5.5.
Cavitation recorded with the HPV-1 high-speed camera at 0.5 Mfps, with simultaneous imaging and focusing the laser pulse through the 50× objective lens. (a) Laser-induced cavitation from a 1.2 mJ laser pulse. (b) Laser-induced cavitation in a pre-established focused ultrasound field of 1.47 MHz and MI = 1.1. Each frame corresponds to a 248 × 248 μm2 area.
(a) Laser-nucleated acoustic cavitation recorded with the Shimadzu HPV-1 camera at 0.5 Mfps with simultaneous imaging and focusing the laser pulse through the 50× objective lens. A 0.95 mJ laser pulse was focused into the focal volume of the ultrasound field of identical parameters to that of Fig. 6(b). Each frame corresponds to a 248 × 248 μm2 area. (b) Laser-nucleated cavitation in a field of higher MI = 3.4, recorded with the Cordin 550–62 high-speed camera at 0.5 Mfps. For this sequence, imaging was performed through the 5× objective, in the orthogonal configuration described in Sec. III, to achieve a larger field-of-view of 672×672 μm2. The laser pulse was focused through the 50× objective.
(a) The acoustic signal recorded from the hydrophone positioned within the cavitation chamber, as depicted in Fig. 5, notch-filtered at 1.47 MHz, recorded during the high-speed images of laser-nucleated cavitation depicted in Fig. 7(b). (i) The spectra of the first 120 μs of the signal and (ii) the remaining 280 μs, during laser-nucleated acoustic cavitation.
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