Laser trapping of cavitation bubbles in liquids

Abstract

Cavitation has a significant impact on pulsed laser ablation of liquids. At high repetition rates of laser pulses, it tends to hinder laser breakdown and associated processes. Here, we report on the particular case of the cavitation process occurring only at the elevated pulse repetition rate — the formation of a laser trapped bubble. The effect was observed in liquid hydrocarbons (n-hexane and ethanol) and water. The cavitation bubbles generated by picosecond pulses were captured in the caustic beam in front of the laser focus and stay there for a long time (several seconds). After growing up to ∼100μm in size, such a bubble completely blocks the laser radiation and stops all processes in the laser waist. The scenario of laser trapped bubble formation is investigated, the effects of pulse energy and pulse repetition rate are analyzed, and a possible mechanism for the observed effect is proposed. The special importance of laser trapped bubbles for the optimization of laser synthesis of new materials, particularly the linear carbon chains in hydrocarbons, is demonstrated.