Effect of nanoscale nuclei on the dynamics of laser-induced cavitation

Abstract

Cavitation inception generally originates from gaseous nuclei in a liquid, either as an air pocket on a solid wall or freely suspended gaseous contaminants. In this work, the impact of nanoscale nuclei, typically around 100 nm in diameter, on laser-induced cavitation is explored. The experimental results indicate that the presence of these nanoscale entities can readily trigger multiple optical breakdowns, resulting in a spark column with essentially discrete character and a train of primary cavitation bubbles nucleating along the laser-focusing path. The investigation further reveals a nuanced relationship between laser pulse energy and cavitation bubble size, moderated by nanoscale nuclei concentration, which ultimately caps the maximal bubble size to approximately 300 μm. The study also delves into the aftermath of initial breakdowns, elucidating the genesis of secondary cavitation through the expansion of both pre-existing and laser-excited nanoscale gaseous nuclei, facilitated by a transient negative pressure field that is formed by the reflection of shock waves on adjacent bubbles' surface. Molecular dynamics simulations demonstrate the scenario at a smaller scale and reveal that the presence of nanobubbles is more conducive to the rupture of the surrounding water under the action of tension waves to generate cavities. This work may lay a foundational framework for future explorations aimed at decrypting the thresholds of cavitation inception, thereby enriching the academic discourse on the control and manipulation of cavitation phenomena within liquid mediums.