  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.
