# Thesis: Experimental exploration of gold semi-continuous films in the near- and far-field

## TL;DR

This thesis explores the optical and plasmonic properties of semi-continuous gold films, revealing their localized hotspots and potential for applications in light enhancement, ultradense data storage, and plasmonic laser printing.

## Contribution

It demonstrates that complex fractal gold films' properties can be understood through localized hotspots and introduces their use in photoluminescence enhancement and laser inscription.

## Key findings

- Localized plasmonic hotspots enhance optical fields thousands of times.
- Gold films can be used for two-photon photoluminescence enhancement.
- Femtosecond laser pulses enable information inscription in the films.

## Abstract

Metallic nanostructures can support so-called plasma oscillations (plasmons). Plasmons allow for the concentration of the energy from light, down to sizes well below the conventional diffraction limit known from optics. Plasmonics thus allows for a plethora of new optical applications at the nanoscale. In this thesis, we have investigated the optical and plasmonic properties of semi-continuous gold films (also called percolation films). These films consist of complex tortuous fractal patterns on the nanoscale. They are an easy, fast, and scalable method to fabricate metallic nanostructures. We show, that despite their very complex overall geometry, a large part of the films' properties can be understood alone based on their strongly localized plasmonic 'hotspots' - areas of just a few nanometres in the films, wherein optical fields are enhanced several thousand times. Additionally, we show that such films can be used for the enhancement of gold two-photon photoluminescence and white light continuum generation. We have also shown that it is possible, via femtosecond-laser pulses, to inscribe information into the films, via phototheral processes. This has potential applications for ultra-dense information storage, and plasmonic colour laser printing.