Bubble dynamics driven by a few successive femtosecond laser pulses in methanol under 1 kHz

The breakdown and related bubble dynamics driven by femtosecond laser pulses in liquid are very critical for the optimization of laser parameters in the applications of medical laser and nano/micro-object manipulation. In this paper, we conduct systematic research on the bubble dynamics in methanol driven by a few successive femtosecond laser pulses under 1 kHz repetition rate. It is demonstrated that it is more probable for two or more successive pulses to induce optical breakdown than only a single pulse. A physical scenario of bubble dynamics from generation to evolution is presented for the successive femtosecond laser pulses interacting with a sample, which also give a reasonable explanation for such a phenomenon. Moreover, the effects of pulse energy and numerical aperture on the optical breakdown and bubble dynamics are investigated and well explained. It is hinted that the laser pulses with high repetition rate (the maximum typically not exceeding the megahertz level so that the cumulative effect of heat cannot be ignored) and low energy and the lens with a large numerical aperture may be an optimal choice for the precise control of the bubble and cutting.