Controlling bubble generation by femtosecond laser-induced filamentation

Femtosecond laser-induced optical breakdown in liquids results in filamentation, which involves the formation and collapse of bubbles. In the present work, we elucidate spatio-temporal evolution, interaction, and dynamics of the filamentation-induced bubbles in a liquid pool as a function of a broad spectrum of laser pulse energies (similar to 1 to 800 mu J), liquid media (water, ethanol, and glycerol), and the number of laser pulses. Filament attributes such as length and diameter have been demarcated and accurately measured by employing multiple laser pulses and were observed to have a logarithmic dependence on laser energy, irrespective of the medium. The size distribution of persisting microbubbles is controlled by varying the pulse energy and the number of pulses. Our experimental results reveal that introducing consecutive pulses leads to strong interaction and coalescence of the pulsating bubbles via Bjerknes force due to laser-induced acoustic field generation. The successive pulses also influence the population density and size distribution of the micro-bubbles. We also explore the size, shape, and agglomeration of bubbles near the focal region by controlling the laser energy for different liquids. The insights from this work on filamentation-induced bubble dynamics can be of importance in diverse applications such as surface cleaning, fluid mixing and emulsification, and biomedical engineering.

Automated summary

In this study, the spatio-temporal evolution, interaction, and dynamics of filamentation-induced bubbles in a liquid pool were investigated by varying laser pulse energies, liquid media, and the number of pulses. The results showed that the length and diameter of the bubbles exhibited a logarithmic dependence on laser energy, regardless of the medium. The size distribution of persisting microbubbles could be controlled by adjusting the pulse energy and the number of pulses. Furthermore, the introduction of consecutive pulses led to strong interaction and coalescence of pulsating bubbles, as well as influencing the population density and size distribution of the micro-bubbles.