Discrimination of effects leading to gas formation during pulsed laser ablation in liquids

Pulsed laser ablation of a bulk target in liquid induces the formation of cavitation bubbles and persistent gas bubbles, which both shield subsequent laser pulses leading to a decrease in nanoparticle productivity. A further shielding entity and a source for gas formation when post-irradiated are the synthesized nanoparticles. In this study, an experimental setup is developed, which allows quantitative measurement of the gas volume produced by these shielding entities. It can be shown that 1 cm³ gas is produced in 10 min ablation time when 8 W picosecond-laser power is applied. By a combined experimental and mathematical approach, the gas volumes induced by silver bulk ablation and post-irradiation effects of the produced colloids are discriminated. It is shown that a characteristic nanoparticle mass concentration threshold exists, where post-irradiation effects mostly dominate gas formation. In a synergistic process, the effective laser fluence available for bulk ablation decreases with increasing nanoparticle mass concentration and up to 80% of the laser power is coupled into the nanoparticles. At the same time, the interparticle distance between the nanoparticles decreases favoring the laser-induced breakdown of the liquid.