Light–matter interaction under intense field conditions: Nonlinear optical properties of metallic-dielectric nanostructures

Background: Metallic–dielectric plasmonic nanoparticles have recently aroused great interest in view of many and novel technological applications, based on the interaction between light and matter under intense field conditions, in nonlinear integrated photonics and opto-fluidics, thanks to the possibility of tuning their electronic and optical properties through a fine control of the synthesis parameters and their nanoparticles under a high-power laser, like the one used during z-scan measures. Objective: The goal of this work is the study of nonlinear optical properties (as nonlinear refraction, scattering, two-photon absorption, optical limiting) of colloids synthesized in different liquid media by Pulsed laser ablation in liquids (PLAL), which is a photo!assisted synthesis technique ensuring the formation of stable, contaminant-free colloids directly during the ablation process. Methods: Noble metal nanoparticles, metal oxides hybrid nanostructures and silicon-based nanomaterials, were prepared by nanosecond and picosecond PLAL technique, in different media. The third-order nonlinear optical (NLO) properties have been studied by the use of a single beam z-scan technique with Q-switched frequency doubled Nd:YAG laser (λ=532 nm) at 5 ns pulse. Results: 1) A good stability of the PLAL nanocolloids under a high laser power; 2) the limiting threshold reduction inducted by the Ag-Au nanoparticles, the increase of the NLO absorption coefficient β, the reduction of the transmittance/scattering signal and the presence of a pronounced asymmetry of the peak/valley profile of the metal decorated metal oxide nanomaterials compared to the separately produced components. Conclusion: An intriguing coupling between the nature of the optical limiting response and the nanostructures rearrangement upon intense field conditions, explaining z-scan data by a classical approach able to account for the nanoparticles asymmetry and plasmonic effects, are the main results found.