# Optical reconfiguration and polarization control in semi-continuous gold films close to the percolation threshold

## TL;DR

This study demonstrates that femtosecond laser pulses can permanently reconfigure semi-continuous gold films, enabling controllable optical and polarization properties for advanced plasmonic applications.

## Contribution

It introduces a method to permanently modify the optical properties of semi-continuous gold films through laser-induced morphological changes, revealing new control over plasmonic behavior.

## Key findings

- Laser writing alters the optical transmission spectra based on wavelength, polarization, and laser intensity.
- Electron energy-loss spectroscopy shows restructuring of plasmonic modes due to photothermal effects.
- The modifications enable scalable, tunable platforms for sensing and data storage.

## Abstract

Controlling and confining light by exciting plasmons in resonant metallic nanostructures is an essential aspect of many new emerging optical technologies. Here we explore the possibility of controllably reconfiguring the intrinsic optical properties of semi-continuous gold films, by inducing permanent morphological changes with a femtosecond (fs)-pulsed laser above a critical power. Optical transmission spectroscopy measurements show a correlation between the spectra of the morphologically modified films and the wavelength, polarization, and the intensity of the laser used for alteration. In order to understand the modifications induced by the laser writing, we explore the near-field properties of these films with electron energy-loss spectroscopy (EELS). A comparison between our experimental data and full-wave simulations on the exact film morphologies hints toward a restructuring of the intrinsic plasmonic eigenmodes of the metallic film by photothermal effects. We explain these optical changes with a simple model and demonstrate experimentally that laser writing can be used to controllably modify the optical properties of these semi-continuous films. These metal films offer an easy-to-fabricate and scalable platform for technological applications such as molecular sensing and ultra-dense data storage.