8,077 research outputs found
Magnetic dipole radiation tailored by substrates: numerical investigation
Nanoparticles of high refractive index materials can possess strong magnetic
polarizabilities and give rise to artificial magnetism in the optical spectral
range. While the response of individual dielectric or metal spherical particles
can be described analytically via multipole decomposition in the Mie series,
the influence of substrates, in many cases present in experimental
observations, requires different approaches. Here, the comprehensive numerical
studies of the influence of a substrate on the spectral response of high- index
dielectric nanoparticles were performed. In particular, glass, perfect electric
conductor, gold, and hyperbolic metamaterial substrates were investigated.
Optical properties of nanoparticles were characterized via scattering
cross-section spectra, electric field profiles, and induced electric and
magnetic moments. The presence of substrates was shown to introduce significant
impact on particle's magnetic resonances and resonant scattering
cross-sections. Variation of substrate material provides an additional degree
of freedom in tailoring properties of emission of magnetic multipoles,
important in many applications.Comment: 10 page, 28 figure
Spin-Hall effect and circular birefringence of a uniaxial crystal plate
The linear birefringence of uniaxial crystal plates is known since the 17th
century, and it is widely used in numerous optical setups and devices. Here we
demonstrate, both theoretically and experimentally, a fine lateral circular
birefringence of such crystal plates. This effect is a novel example of the
spin-Hall effect of light, i.e., a transverse spin-dependent shift of the
paraxial light beam transmitted through the plate. The well-known linear
birefringence and the new circular birefringence form an interesting analogy
with the Goos-H\"anchen and Imbert-Fedorov beam shifts that appear in the light
reflection at a dielectric interface. We report the experimental observation of
the effect in a remarkably simple system of a tilted half-wave plate and
polarizers using polarimetric and quantum-weak-measurement techniques for the
beam-shift measurements. In view of great recent interest in spin-orbit
interaction phenomena, our results could find applications in modern
polarization optics and nano-photonics.Comment: 16 pages, 8 figures, to appear in Optic
Nonparametric estimation of the heterogeneity of a random medium using Compound Poisson Process modeling of wave multiple scattering
In this paper, we present a nonparametric method to estimate the
heterogeneity of a random medium from the angular distribution of intensity
transmitted through a slab of random material. Our approach is based on the
modeling of forward multiple scattering using Compound Poisson Processes on
compact Lie groups. The estimation technique is validated through numerical
simulations based on radiative transfer theory.Comment: 23 pages, 8 figures, 21 reference
Benchmark problems for continuum radiative transfer. High optical depths, anisotropic scattering, and polarisation
Solving the continuum radiative transfer equation in high opacity media
requires sophisticated numerical tools. In order to test the reliability of
such tools, we present a benchmark of radiative transfer codes in a 2D disc
configuration. We test the accuracy of seven independently developed radiative
transfer codes by comparing the temperature structures, spectral energy
distributions, scattered light images, and linear polarisation maps that each
model predicts for a variety of disc opacities and viewing angles. The test
cases have been chosen to be numerically challenging, with midplane optical
depths up 10^6, a sharp density transition at the inner edge and complex
scattering matrices. We also review recent progress in the implementation of
the Monte Carlo method that allow an efficient solution to these kinds of
problems and discuss the advantages and limitations of Monte Carlo codes
compared to those of discrete ordinate codes. For each of the test cases, the
predicted results from the radiative transfer codes are within good agreement.
The results indicate that these codes can be confidently used to interpret
present and future observations of protoplanetary discs.Comment: 15 pages, 10 figures, accepted for publication in A&
Near-field Optical Interactions And Applications
The propagation symmetry of electromagnetic fields is affected by encounters with material systems. The effects of such interactions, for example, modifications of intensity, phase, polarization, angular spectrum, frequency, etc. can be used to obtain information about the material system. However, the propagation of electromagnetic waves imposes a fundamental limit to the length scales over which the material properties can be observed. In the realm of near-field optics, this limitation is overcome only through a secondary interaction that couples the high-spatial-frequency (but non-propagating) field components to propagating waves that can be detected. The available information depends intrinsically on this secondary interaction, which constitutes the topic of this study. Quantitative measurements of material properties can be performed only by controlling the subtle characteristics of these processes. This dissertation discusses situations where the effects of near-field interactions can be (i) neglected in certain passive testing techniques, (ii) exploited for active probing of static or dynamic systems, or (iii) statistically isolated when considering optically inhomogeneous materials. This dissertation presents novel theoretical developments, experimental measurements, and numerical results that elucidate the vectorial aspects of the interaction between light and nano-structured material for use in sensing applications
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