Hopkins, Benjamin Thomas
Description
The study of nanostructured artificial media for optics has
expanded rapidly over the last few decades, coupled with
improvements of fabrication technology that have enabled
investigation of previously unrealisable optical scattering
systems. Such development is complemented by renewed impetus to
understand the physics of optical scattering from
complex subwavelength geometry and nanoparticle systems. Here I
investigate speci
cally the optical properties of...[Show more] closely packed
arrangements of nanoparticles, known as nanoparticle oligomers,
which provide an intuitive platform for analytical and numerical
study on the formation and interplay of collective resonances. I
consider both plasmonic nanoparticles, and also
high-refractive-index dielectric nanoparticles that support
Mie-type electric and magnetic dipole resonances. Specifi c
outcomes of this study are listed as follows. (i) A new model is
presented for optical Fano resonances, which is based on
interference between nonorthogonal eigenmodes of the associated
scattering object. This is demonstrated to correctly describe
Fano resonances in both plasmonic and high-refractive-index
dielectric
nanoparticle oligomers; it also revealed capacity for two-channel
Fano interference in the magnetic dipolar response from the
dielectric oligomers. (ii) Polarisation-independent scattering
and absorption losses are shown to be enforced by n-fold discrete
rotational symmetry, Cn (n \geq 3), and reciprocal degeneracy of
eigenmodes. (iii) A new form of
circular dichroism is presented, which occurs due to the
interaction of nonorthogonal resonances, and impacts the ratio of
radiative scattering loss to dissipative absorption loss
experienced by reciprocal plane waves. Geometric asymmetry and
optical chirality are also reviewed to quantify the minimum
symmetries that must be broken to allow other circular dichroism
effects in chiral and achiral scattering objects. The sequence of
general theoretical conclusions (i)-(iii) serve to build the
understanding of optical scattering from nanoparticle systems
while removing existing ambiguities.
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