Exploring combinations of spatial laser beam shaping for advancing nanoparticle synthesis by ablation in liquids

Pulsed laser ablation in liquids (PLAL) is a versatile and sustainable technique for the synthesis of ligand-free colloidal nanoparticles, but its wider application is limited by relatively low productivity and insufficient control over particle size distributions. Here, to advance the technique, we investigate the possibility of combining in one synthesis process the advantages of two recently developed cost-effective approaches, multibeam PLAL for productivity increase and donut-shaped laser beams for particle size modification. Nanoparticles of gold, an iron–nickel alloy, and a high-entropy alloy were produced in water using single-beam and multibeam configurations with four and eleven picosecond sub-beams. The effects of beam profile, beam-splitting factor, and laser fluence on particle yield and size distributions were systematically evaluated. Splitting donut-shaped beams is shown to offer a similar productivity increase as Gaussian pulses, and, at moderate fluences, multiple donut beams can be even more efficient. A single donut-shaped beam generally reduces the particle size, but, in a multibeam configuration, the reduction effect is hindered by secondary processes such as the interaction of cavitation bubbles, nanoparticle fragmentation, and redeposition. The results demonstrate the feasibility of combining donut-shaped beams with multibeam ablation in PLAL synthesis and identify key process parameters that have to be optimized to achieve both high productivity and improved particle size control.