Bubble dynamics in metal nanoparticle formation by laser ablation in liquid studied through high-speed laser stroboscopic videography

Laser ablation in liquid (LAL) is utilized in many applications, such as the fabrication of nanoparticles, laser cleaning and laser peening. We have developed a high-speed laser stroboscopic videography system that enables observations at intervals of 1 μs. Using this imaging system, we investigated the dynamics of cavitation bubbles induced by LAL to elucidate the timing and location of nanoparticle formation and dispersion into the surrounding liquid. The initial bubble demonstrated a well-defined, smooth boundary during its growth and shrinkage. Although previous studies have reported the ejection of particles at the boundary of the bubble, this was not observed in our images. Intermixing between the gas phase of the bubble and the surrounding liquid occurred when the first bubble collapsed. Jet-like shadows were recorded during LAL in water after multiple-pulse irradiation, but were not observed in freshly filled water that had not yet been irradiated. These shadows disappeared within 10 μs and are postulated to be micro-bubbles induced by interactions between nanoparticles suspended in the water and the incoming laser beam.