Plasmon guided assembly of nanoparticles in solids

Light manipulation of metallic nanoparticles (NPs) with outstanding plasmonic properties attracts broad interest in multiple areas owing to the significant field enhancement and localization effect mediated by plasmons. So far, optical migration of NPs has only been achieved on platforms such as gases, solutions, and mesoporous thin films (TiO2), while not been realized for NPs inside large macroscopic transparent materials due to the high density and viscosity of a host matrix. The high localization of light intensity by plasmons allows the laser pulses to deposit energy via near-field at the nanoscale at reduced thermal modification and ablation over extended regions inside a host material. This makes it possible to achieve directed and guided migration of NPs within large macroscopic transparent materials. Here, we propose a plasmon-enhanced method using ultrafast laser direct writing to manipulate metal NPs inside a glass. The optical potential between closely spaced NPs increases significantly under laser irradiation, leading to guided energy deposition by ionization, and light interference which leads to the self-assembly of NPs into nanostructures under irradiation of subsequent pulses. In this work, ordered subwavelength NP gratings are fabricated, which exhibit polarization dependence and show promise for applications in information encoding and optical storage. This study provides a new physical case for ultrafast laser-driven guided self-assembly of NPs, where the dynamic evolution via their fragmentation and migration is observed, contributing to the understanding of the origin of self-assembled gratings and opening up new research directions for light manipulation of NPs.