简介：Abstract The laser-induced cavitation in water or soft materials is of great importance in various applications including low-invasive medical treatments. This lecture overviews recent experimental investigation on the cavitation, with focusing on following three topics: (i) shockwave generation and bubble expansion right after the laser illumination, (ii) bubble shrink with forming a liquid jet, and (iii) stress waves induced by bubble collapse. (i) First we examine a laser-induced underwater shock wave paying special attention to the pressure impulse, the time integral of the pressure evolution using a combined measurement system that obtains high-resolution nanosecond-order image sequences. Remarkably, the pressure impulse is found to be symmetrically distributed for a wide range of experimental parameters, even when the shock waves are emitted from an elongated region. Based on this unique property, we investigate the effect of a shockwave on the velocity of a microjet and underwater cavitation onset in a microchannel. The experimental results suggest that the jet velocity depends only on the pressure impulse of the shockwave, while the probability of cavitation onset depends only on the peak pressure of the shockwave. (ii) We experimentally investigate the bubble collapse and jet formation in corners formed of two flat solid boundaries with different opening angles. Using potential flow analysis, we accurately predict the direction of the jet and bubble displacement, covering the full range of corners from the limiting case of a bubble near a single wall (n = 1) up to a bubble in between parallel walls (n→∞). (iii) Using elastographic imaging and high-speed imaging, we find that cavitation in elastic solids may emit shear waves that could affect soft tissues in human bodies/brains. During the collapse of the cavity close to an air-solid boundary, the cavity moves away from the boundary and forms a directed jet flow, which confines shear stresses in a volume between the bubble and the free boundary. References: - Tagawa, Y., Yamamoto, S., Hayasaka, K., and Kameda, M., On pressure impulse of a laser-induced underwater shock wave, Journal of Fluid Mechanics, 808, pp. 5-18 (2016). - Hayasaka, K., Kiyama, A., and Tagawa, Y., Effects of pressure impulse and peak pressure of a shockwave on microjet velocity in a microchannel, Microfluidics and Nanofluidics, 21:166 (2017). - Tagawa, Y., and Peters, I. R., Bubble collapse and jet formation in corner geometries, Physical Review Fluids, 3, 081601(R), (2018). - Rapet, J., Tagawa, Y., and Ohl, C.D., Shear-wave generation from cavitation in soft solids, Applied Physics Letters, 114, 123702, (2019). 报告人介绍：Brief Biography Yoshiyuki Tagawa did his undergraduate and graduate studies at The University of Tokyo in Japan.  He was a Japan Society for the Promotion of Science Research Fellow at The University of Tokyo and a postdoctoral fellow at the University of Twente in the Netherlands. Dr. Tagawa is currently Associate Professor in the Dept. Mechanical Systems Engineering at the Tokyo University of Agriculture and Technology (TUAT). Dr. Tagawa has received many awards such as Andrea Prosperetti Award 2019 in ICMF, Distinguished Young Researcher 2014 in The Japan Society of Fluid Mechanics, among others. Dr. Tagawa is also a great educator. In recent 6 years, students under his supervision won more than 30 presentation awards. Successful 4 PhD students are already graduated during his career of 6 years in TUAT, where two of his PhD students won competitive Research Fellowships for Young Scientists (DC1) from JSPS. His research projects are highly valued as he won the highly ranked grants in Japan, e.g. Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (A), Grant-in-Aid for Young Scientists (A).