Abstract:
The coupled oscillations of free electrons and the optical waves at the metal-dielectric
interfaces are known as surface plasmons. This kind of light-matter interaction in plasmonic
nanostructures has made it possible to realize the concept of optical antennae.
These are the devices which can work as a transducer between free radiation and localized
source. An optical antenna can be characterized by two main properties: a)
ability to localize optical fields to sub-wavelength scales and b) the ability to spatially
redirect the near-field emissions. Localization of fields is important for obtaining enhanced
interactions with nearby molecules; whereas, defined directionality is useful to
increase detection efficiency. Here in this thesis, we will present how the two fundamental
excitations of surface plasmons i.e., (i) localized surface plasmon (LSP) and (ii)
propagating surface plasmon polaritons (SPP) can be utilized to obtain field localization
and well defined directional emission at plasmonic nanojunctions, which in turn work
as optical antennae.
First, we shall present how the LSP mediated field localization at the junction of
a Palladium (Pd) bridged gold (Au) nanocylinder dimer can be tuned by varying the
geometrical parameters of the system and how this geometry can be used for efficient
hydrogen detection.
Next, we will present how the propagating SPP in silver (Ag) nanowire (NW), generated
due to terminal optical excitation of the wire; can lead to field localization at a
serially-coupled Ag NW- dimer junction or a NW-nanoparticle junction which is spatially
separated from the excitation point. We will also show that the efficient SPP
waveguiding through the NW results in directional scattering of light at the coupled
NW dimer junction. Furthermore, we will show how these phenomena can be employed
to remotely excite molecules placed at the junctions and influence directional
emission from them.
