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Light Management for Engineering Luminescence in Nanoscale Environments By Numerical Optimization
(2018)
Benchmarking five computational methods for analyzing large photonic crystal membrane cavities
(2017)
The interaction of light and chiral matter is subject of recent research both in fundamental science and applications.
Among these are the helicity of electromagnetic fields described with the optical chirality density and emitters sensitive to
circular polarization employed in quantum communications.
In the weak coupling regime of chiral emitters, we analyze the conversion of chirality which can be regarded as an analogue
to absorption of energy describing the change of circular polarization of the incident field. This enables the tailoring of
chiral near-fields close to metamaterials, e.g. composed of gold helices, and gives insights into extinction measurements
such as circular dichroism.
We show relation of the weak and strong coupling regime. The latter can be modelled with cross electric-magnetic polarizabilities or
with effective chiral materials, i.e. bi-anisotropic media. Accordingly, we motivate the necessity for rigorous numerical
simulations to accurately describe chiral light-matter interaction.
The helicity of light is of great interest
in both fundamental research and in applications such as dichroism spectroscopy. Its
time-harmonic formulation is directly proportional to the density of optical chirality.
Recently, both an helicity optical theorem
(HOT) and a chirality conservation law
(CCL) have been formulated for arbitrary
scatterers taking into account an underlying
continuity equation of this quantity. We
summarize these two equivalent fundamental laws and analyze their potential applications.
The introduction of the near-field quantity of optical chirality has emerged in various numerical and few experimental studies of local chirality enhancement due to its relation to the excitation rate of chiral molecules. This time-even pseudoscalar has been dismissed as being a higher-order version of helicity. Nevertheless, we revisit the derivation of the underlying conservation law and define optical chirality in media similar to. We identify the mechanism of chirality conversion by either inhomogeneous or anisotropic space to complement the conservation of optical chirality.
The conservation law of optical chirality in arbitrary space enables the extension of the concept of polarization to the near-field where no distiniguished propagation direction of light is present. We show that the connection of electromagnetic energy and optical chirality provide the ability to define a circular polarization basis in time-harmonic near-field analysis.
In order to illustrate our theory, we present electromagnetic field simulations of simple as well as more complex nanostructures. Results using the well-known far-field polarization concept are readily reproduced and extended from the point of view of chirality conversion.
Strong and directionally specific forward scattering from optical nanoantennas is of utmost importance for various applications in the broader context of photovoltaics and integrated light sources. Here, we outline a simple yet powerful design principle to perceive a nanoantenna that provides directional scattering into a higher index substrate based on the interference of multiple electric dipoles. A structural implementation of the electric dipole distribution is possible using plasmonic nanoparticles with a fairly simple geometry, i.e. two coupled rectangular nanoparticles, forming a dimer, on top of a substrate. The key to achieve directionality is to choose a sufficiently large size for the nanoparticles. This promotes the excitation of vertical electric dipole moments due to the bi-anisotropy of the nanoantenna. In turn, asymmetric scattering is obtained by ensuring the appropriate phase relation between the vertical electric dipole moments. The scattering strength and angular spread for an optimized nanoantenna can be shown to be broadband and robust against changes in the incidence angle. The scattering directionality is maintained even for an array configuration of the dimer. It only requires the preferred scattering direction of the isolated nanoantenna not to be prohibited by interference.