Control of Scattering and Absorption of Light by Multilayer Nanowires
Date
2016
Authors
Mirzaei, Ali
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Abstract
In recent decades, nanotechnology has become one of the biggest
steps forward in expanding the horizons of science and
engineering. Nanotechnology progressively plays more important
roles in various modern technologies that are revolutionising
human lifestyle. Nano-photonics as one of the fastest growing
fields in nanotechnology, is finding its way to become a key tool
in various applications. This involves variety of scientific and
technological problems, from medical diagnosis and cancer therapy
to ultrafast computation and data communication. However,
continuously improving cutting-edge technology of optical
nanostructures, requires further development of analysis for
designing more advanced nanostructures for future generations of
optical nano-devices.
The reported progress in nanophotonics, is mainly based on
advances in theoretical optics and experimental techniques.
Numerical simulations and experiments have made a significant
progress in analysing and designing optical nanostructures for
various applications. However, they both become considerably
expensive in terms of time and material especially when they have
to be repeated for several times to optimise a set of parameters.
Furthermore, repeatability and measurement challenges in
experiments, and robustness and finite precision complications in
simulations, yet remain. These restrictions, consequently, limit
the exploration possibility for new ideas and solutions for
future nanophotonics.
To address this, I introduce a novel, fast and exact approach by
employing analytical/semianalytical solutions and powerful
optimisation techniques without the mentioned restrictions. This
approach suggests a novel platform for wide exploration of unique
possibilities for developing new ideas. I discuss the details of
my approach by employing multilayer nanostructures for example
applications in optics. To achieve optimal performance, I develop
a smart optimisation process that employs the fast analytical
solutions within a genetic algorithm. I explain the details of
this process that can optimise complicated structures by
exploring multi-dimensional parameter space in both linear and
nonlinear regimes.
My proposed approach, can generally be applied for different
types of nanostructures with different geometries. However, among
various introduced components, nanowires have proven themselves
to be appropriate candidates for taking important roles in
optical devices for different applications. In addition, by
studying long nanowires, I analyse optical nanostructures using
the developed semi-analytical approach in a two-dimensional
platform. Therefore, we can concentrate on developing the main
concepts by avoiding unnecessary complications. In this thesis I
provide the complete analysis of nanowire with large aspect
ratios, however our further studies prove that the developed
design solution and achieved results are not restricted to
two-dimensional platform, and are also applicable for
three-dimensional structures. I briefly discuss this with some
examples, such as nanodisks and nanospheres, even in more
complicated configurations and by presence
of substrates.
To discuss the details, after a brief introduction in Chapter 1,
I first discuss two parallel approaches in Chapter 2: (i) a
semi-analytical method to analyse the scattering and absorption
of light with single and interfering multilayer nanowires, and
(ii) a smart genetic optimisation algorithm, employing the fast
semi-analytical solution to search for optimal set of designing
parameters.
Then, I focus on developing specific structures based on
multilayer nanowire systems. Controlling the light-matter
interaction in nanowires allows to engineer the scattering and
absorption efficiencies, with the possibility to enhance or
suppress the corresponding cross section. As examples, I discuss
invisibility cloaking and superscattering of light as two
oppositely different effects in Chapter 3. Enhancing the
absorption of light on the other hand, is important for improving
the efficiency of many optical devices which in its extremum
case, can cause superabsorption effect. This is also discussed in
detail by the use of single multilayer nanowires in Chapter 3.
By bringing more nanowires together and constructing more
complicated systems, the interference between the nanowires can
lead to remarkable effects. In Chapters 2 and 4, I explain the
analytical solution of multiple scattering problems in nanowire
systems. Example structures in Chapter 4 demonstrate that
carefully controlling the behaviour of light in nanowire dimer
systems can lead us to manage electric and magnetic hotspots, and
a complex nanowire system to electromagnetically shield
non-isolated areas.
Finally, going beyond the linear regime, I discuss nonlinear
effects in multilayer nanowires in Chapter 5, by introducing my
novel semi-analytical recipe. By studying an example of nonlinear
superscattering of light by a core-shell nanowire and its
hysteresis loop and bistability, I demonstrate that my approach
is accurate and more than 100,000 times faster than finite
difference time domain.
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Optic, nanowire, scattering, absorption, dielectric, plasmonic, multilayer, optimization
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