Microparticle laser fragmentation in liquids: mechanisms, energetics, and efficiency quantified with single-pulse, single-particle precision

In addition to nanoparticle laser fragmentation in liquids, laser fragmentation of readily available microparticles in liquids has emerged as a promising approach to generate nanoparticles with high efficiency. Despite its advantages, the underlying fragmentation mechanisms, their influence on the nanoparticle size distribution, and the energy efficiency of the process remain poorly understood. In this study, microparticle fragmentation is investigated in single-pulse, single-particle experiments on Au microparticles. Determining the absorbed peak fluence enables an assessment of the process energetics. Pump–probe microscopy in conjunction with nanoparticle size analysis using transmission electron 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 energy, while only 2 % is converted into surface energy. The surface energy generated per absorbed laser energy is 20 times higher, and the overall energy efficiency is 30 times higher than for laser ablation of bulk Au in water. This gain originates from the confined microparticle geometry, which 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.