Size control of nanoparticles synthesized by pulsed laser ablation in liquids using donut-shaped beams.

The potential to modify the size distribution of nanoparticles synthesized by pulsed laser ablation in liquids is demonstrated using a donut-shaped laser beam. In experiments on pulsed laser ablation in water of gold, yttrium oxide, and high-entropy alloy targets with both Gaussian and donut-shaped beams, we observed a significant reduction in particle size, narrowing of the size distribution width, and an improvement in sphericity when utilizing the donut-shaped laser beam. We performed time-resolved shadowgraph imaging of the laser-induced cavitation bubble, revealing a toroidal structure that overruns the ring-shaped ablation site, compared to the quasi-hemispherical bubble covering the ablation spot produced by the Gaussian beam. Based on this pioneering study, further investigation with higher temporal and spatial resolution are warranted.