Enhancing laser-nanoparticle interactions by diffused laser beams: efficient size-reduction of nanoparticles

Abstract

Generally speaking, a laser beam with a good spatial profile such as flat-top or Gaussian (TEM00 mode) shape is considered to be a prerequisite to maximize laser-matter interactions. On the contrary, we show that if the process of interest has a threshold in terms of laser fluence or intensity, a diffused laser beam can do a good job of inducing the process. As an example, we demonstrate the efficient size-reduction of colloidal nanoparticles by a diffused laser beam and identify that the physical origin of this counterintuitive results is a redistribution of laser energy, i.e. formation of speckles through a diffuser where the local laser fluence exceeds the size-reduction threshold. We report the systematic results for silver and gold nanoparticles.