Light-matter interaction mediated by localised and propagating surface plasmons
File(s)
Author(s)
Mota, Monica
Type
Thesis
Abstract
Understanding how light-matter interactions can be enhanced is the central theme of much of
solid state physics research currently. The potential applications of being able to harness and
control light at the nano scale would bring about a new generation of devices the likes of which
have not been seen since the infancy of silicon based electronics. Such applications touch all the
sciences, from information processing in optical quantum computing to magnetic data storage,
single molecule sensing, more efficient solar cells and even highly localised cancer therapy.
Surface plasmons are one of the most promising approaches to this end. At their most fundamental
level they are electromagnetic waves - light - coupled to conduction electrons of a
metallic material that can both propagate and locally resonate in structures much smaller than
the wavelength of visible light. These properties, when combined with careful design and material
choice, lead to nano structures that are capable of creating regions with fields many orders
of magnitudes more intense than free space in volumes smaller than the diffraction limit. Antennas
with gaps on the scale of nanometers are able to produce such an environment via plasmons,
with much stronger fields than any other structure. When combined with waveguides, structures
designed to transport light as efficiently as possible, then a myriad of different devices can be
created.
This thesis examines a specific set of plasmonic structures, namely bar antennas, gap plasmon
waveguides and dimer antennas. In particular, it examines the coupling of light from a focussed
beam to a nanogap plasmonic waveguide via a dimer antenna coupling approach. It will be
shown how these were analysed from a phenomenological approach by modelling their response
with classical coupled oscillators, measuring their spectral behaviour via their extinction cross
sections and their design optimised for maximum incoupling of free space radiation in the the
waveguide in the visible regime. The most efficient design was identified and its response
experimentally measured, where the free space coupling efficiency was found to be 28%, in
agreement with theoretical simulations. Computer vision algorithms were employed to automate
the image processing of hundreds of experimental measurements. A characterisation tool to map
the near fields of such devices is also introduced, cathodoluminescence, whose resolution is only
limited by the focal spot of an electron beam. A new way way of imaging using this tool maps
the reciprocal space of the local density of optical states and can be acquired in a single shot
in only a few seconds.
solid state physics research currently. The potential applications of being able to harness and
control light at the nano scale would bring about a new generation of devices the likes of which
have not been seen since the infancy of silicon based electronics. Such applications touch all the
sciences, from information processing in optical quantum computing to magnetic data storage,
single molecule sensing, more efficient solar cells and even highly localised cancer therapy.
Surface plasmons are one of the most promising approaches to this end. At their most fundamental
level they are electromagnetic waves - light - coupled to conduction electrons of a
metallic material that can both propagate and locally resonate in structures much smaller than
the wavelength of visible light. These properties, when combined with careful design and material
choice, lead to nano structures that are capable of creating regions with fields many orders
of magnitudes more intense than free space in volumes smaller than the diffraction limit. Antennas
with gaps on the scale of nanometers are able to produce such an environment via plasmons,
with much stronger fields than any other structure. When combined with waveguides, structures
designed to transport light as efficiently as possible, then a myriad of different devices can be
created.
This thesis examines a specific set of plasmonic structures, namely bar antennas, gap plasmon
waveguides and dimer antennas. In particular, it examines the coupling of light from a focussed
beam to a nanogap plasmonic waveguide via a dimer antenna coupling approach. It will be
shown how these were analysed from a phenomenological approach by modelling their response
with classical coupled oscillators, measuring their spectral behaviour via their extinction cross
sections and their design optimised for maximum incoupling of free space radiation in the the
waveguide in the visible regime. The most efficient design was identified and its response
experimentally measured, where the free space coupling efficiency was found to be 28%, in
agreement with theoretical simulations. Computer vision algorithms were employed to automate
the image processing of hundreds of experimental measurements. A characterisation tool to map
the near fields of such devices is also introduced, cathodoluminescence, whose resolution is only
limited by the focal spot of an electron beam. A new way way of imaging using this tool maps
the reciprocal space of the local density of optical states and can be acquired in a single shot
in only a few seconds.
Version
Open Access
Date Issued
2021-07
Date Awarded
2022-03
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Oulton, Rupert
Maier, Stefan
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)