Parametric optimization of energy conversion and hydrodynamic interactions for tapered fiber laser-induced cavitation bubble propulsion

This study proposes a non-contact microscale propulsion strategy that employs a tapered-optical-fiber-mediated laser-induced cavitation bubbles to achieve precise microsphere manipulation in aqueous environments. By shaping and focusing laser pulses through a tapered optical fiber, plasma generation, and bubble dynamics are induced near the focal point. Through optimization of laser energy and bubble-microsphere initial distance, the efficiency of underwater microsphere propulsion is significantly enhanced. The parameter studies further determine that when the laser energy is constant, there is an optimal initial distance between the bubble and the microsphere to maximize the propulsion efficiency. The maximum instantaneous pulse coupling coefficient and the microsphere thrust increase first and then decrease with the increase of initial distance. We distinguish two different propulsion mechanisms based on the contact state between the bubble and the microsphere: in non-contact scenarios, liquid inertia governs microsphere motion, whereas direct momentum transfer becomes predominant upon bubble and microsphere surface contact. By integrating energy regulation with spatial matching strategies, this work establishes dual optimization criteria for non-contact microscale propulsion systems. These findings contribute to providing theoretical support and application for laser propulsion in simulated seawater environment and targeted transport based on microfluidic chips by resolving critical hydrodynamic interaction challenges.