Effects of liquid depth on the expansion and collapse of a hemispherical cavitation bubble induced in nanosecond pulsed laser ablation of a solid in liquid

This study examines the growth and collapse dynamics of a cavitation bubble induced by nanosecond pulsed laser ablation of a solid in finite liquid depths. The investigation was conducted with liquid depths that varied from 0.4 to 9 times the maximum bubble radius. The bubble dynamics were tracked using a high-speed laser stroboscopic videography system in the photoelasticity mode. When the liquid depth is sufficiently smaller than the maximum bubble radius, the bubble bursts through the liquid layer during its expansion. The bubble lifetime is substantially shortened, and no secondary shock is detected. At liquid depths that range from slightly below to twice the maximum bubble radius, the bubble is elongated during its expansion and flattened during its shrinkage. The bubble is toroidal at minimum contraction, which leads to multiple emissions of secondary shock waves. In comparison to the bubble lifetime calculated by the Rayleigh-Plesset model, the lifetime of a bubble developed in a finite liquid depth is shortened by a factor that is a function of the non-dimensional liquid depth measured by the maximum bubble radius. These findings contribute to increasing the control and the productivity of applications for nanosecond pulsed laser ablation in liquid.