Investigation of the time to formation of laser-induced cavitation bubbles in water
Egor D. Tulnikov1,2, Nikita V. Kovalenko1,2, Oleg A. Ryabushkin1,2; 1Moscow Institute of Physics and Technology, Moscow, Russia, 2NTO IRE-Polus, Moscow, Russia
Abstract
This work investigated the time to formation of laser-induced cavitation bubbles at the tip of an optical fiber immersed in water. The appearance of the cavitation bubble was determined by the change in the backscattered signal, caused by the change in the reflecting boundary from glass-water to glass-vapor. The wavelength of the incident radiation was 1.5 μm, and the average power in the pulse varied in the range of 3-10 W. For a given incident radiation power, 100 measurements were performed, the results of which were averaged. The measurement results showed that the time to cavitation bubble formation decreases with increasing average power in the pulse according to a complex law, which at high powers approaches a hyperbolic dependence.
Also, in this work, to estimate the time to the appearance of the cavitation bubble, the problem of heating water to boiling point was considered, taking into account boiling point’s change due to pressure growth. The continuity equation, the Euler equation of fluid motion, the heat and mass transfer equation, and the Nobel-Abel equation of state for water were used to describe the process. For simplicity of calculations, the problem was considered in one dimension, viscosity and thermal conductivity were not taken into account. At high incident radiation powers (~7-10 W), the simulation results are consistent with experimental results. The results obtained in this work can be used to optimize the radiation parameters in laser lithotripsy in order to reduce the retro-pulse effect of kidney stones.
Speaker
Tulnikov Egor
NTO IRE-Polus, MIPT
Russia
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