Microparticle laser fragmentation in liquids: mechanisms, energetics, and efficiency quantified with single-pulse, single-particle precision
Microparticle laser fragmentation in liquids has emerged as a promising approach to generate nanoparticles with high efficiency. Despite its advantages, the underlying fragmentation mechanisms, their connection to the nanoparticle size distribution, and the energy efficiency of the process remain poorly understood. In this study for the first time, microparticle fragmentation is investigated in single-pulse, single-particle experiments on Au microparticles. Determining the absorbed peak fluence enables assessment of the process energetics. Pump-probe microscopy identifies photomechanical fracture of the molten microparticle volume and photothermal phase explosion of its superheated surface as the fragmentation mechanisms. We find that 83% of the absorbed laser energy is converted into cavitation bubble formation, while only 1% contributes to the surface energy of the generated nanoparticles. Despite this small fraction, MP-LFL outperforms laser ablation in liquids. The surface energy generated per absorbed energy is 10 times higher, and the overall energy efficiency is 14 times higher. This gain originates from the confined microparticle geometry, which minimizes energy losses and enhances photomechanical fragmentation via pressure focusing. These results position microparticle fragmentation in liquids as a fundamentally more energy-efficient approach for scalable, laser-based nanoparticle production than laser ablation in liquids.