Amplification of high-intensity pressure waves and cavitation in water using a multi-pulsed laser excitation and black-TiOx optoacoustic lens

• Published in: Biomedical optics express Vol. 13; no. 7; pp. 3993 - 4006
• Main Authors: Tašič Muc, Blaž, Vella, Daniele, Lukač, Nejc, Kos, Matjaž, Jezeršek, Matija
• Format: Journal Article
• Language: English
• Published: Optica Publishing Group 01.07.2022
• ISSN: 2156-7085; 2156-7085
• DOI: 10.1364/BOE.460713

A method for amplification of high-intensity pressure waves generated with a multi-pulsed Nd:YAG laser coupled with a black-TiOx optoacoustic lens in the water is presented and characterized. The investigation was focused on determining how the multi-pulsed laser excitation with delays between 50 µs and 400 µs influences the dynamics of the bubbles formed by a laser-induced breakdown on the upper surface of the lens, the acoustic cavitation in the focal region of the lens, and the high-intensity pressure waves generation. A needle hydrophone and a high-speed camera were used to analyze the spatial distribution and time-dependent development of the above-mentioned phenomena. Our results show how different delays ( t d ) of the laser pulses influence optoacoustic dynamics. When t d is equal to or greater than the bubble oscillation time, acoustic cavitation cloud size increases 10-fold after the fourth laser pulse, while the pressure amplitude increases by more than 75%. A quasi-deterministic creation of cavitation due to consecutive transient pressure waves is also discussed. This is relevant for localized ablative laser therapy.