Pulse-interval-dependent cavitation bubble expansion for high-speed particle manipulation by femtosecond laser irradiation

Focused irradiation of femtosecond laser pulses into an aqueous solution induces cavitation bubbles (CBs) through explosive water vaporization, generating impulsive forces that can be harnessed for particle manipulation. For applications such as high-speed cell sorting, achieving controllable and sufficiently large forces is essential. Multiple-pulse irradiation provides an effective and feasible approach, as each CB undergoes microsecond-scale expansion and contraction, producing alternating push–pull forces. In this study, we investigated the effect of pulse-to-pulse intervals (up to 12 μs) on particle displacement, enabling selective enhancement of the net force under the double pulse irradiation case. Optimized intervals of 10 μs for beads and cells were identified. The results demonstrate that dual CBs via double-pulse irradiation allow rapid and controllable manipulation of microparticles, offering a powerful strategy for high-speed, flexible cell handling in microfluidic devices, including separation and sorting.