Proceedings Article | 29 February 2016
KEYWORDS: Cavitation, Calculus, Pulsed laser operation, High speed cameras, Laser lithotripsy, Laser therapeutics, Laser processing, Laser energy, Absorption, Liquids, Fiber lasers, Oscilloscopes
Although laser lithotripsy is now the preferred treatment option for urolithiasis, the mechanism of laser pulse induced
calculus damage is still not fully understood. This is because the process of laser pulse induced calculus damage
involves quite a few physical and chemical processes and their time-scales are very short (down to sub micro second
level). For laser lithotripsy, the laser pulse induced impact by energy flow can be summarized as: Photon energy in the
laser pulse → photon absorption generated heat in the water liquid and vapor (super heat water or plasma effect) →
shock wave (Bow shock, acoustic wave) → cavitation bubble dynamics (oscillation, and center of bubble movement ,
super heat water at collapse, sonoluminscence) → calculus damage and motion (calculus heat up, spallation/melt of
stone, breaking of mechanical/chemical bond, debris ejection, and retropulsion of remaining calculus body). Cavitation
bubble dynamics is the center piece of the physical processes that links the whole energy flow chain from laser pulse to
calculus damage. In this study, cavitation bubble dynamics was investigated by a high-speed camera and a needle
hydrophone. A commercialized, pulsed Ho:YAG laser at 2.1 mu;m, StoneLightTM 30, with pulse energy from 0.5J up to 3.0
J, and pulse width from 150 mu;s up to 800 μs, was used as laser pulse source. The fiber used in the investigation is
SureFlexTM fiber, Model S-LLF365, a 365 um core diameter fiber. A high-speed camera with frame rate up to 1 million
fps was used in this study. The results revealed the cavitation bubble dynamics (oscillation and center of bubble
movement) by laser pulse at different energy level and pulse width. More detailed investigation on bubble dynamics by
different type of laser, the relationship between cavitation bubble dynamics and calculus damage
(fragmentation/dusting) will be conducted as a future study.
