85 research outputs found
Spherically symmetric inhomogeneous bianisotropic media: Wave propagation and light scattering
We develop a technique for finding closed-form expressions for electromagnetic fields in radially inhomogeneous bianisotropic media, both the solutions of the Maxwell equations and material tensors being defined by the set of auxiliary two-dimensional matrices. The approach is applied to determine the scattering cross-sections by spherical particles, the fields inside which correspond to the Airy-exponential waves
Tailored optical potentials for Cs atoms above waveguides with focusing dielectric nano-antenna
Tuning the near-field using all-dielectric nano-antennae offers a promising
approach for trapping atoms, which could enable strong single-atom/photon
coupling. Here we report the simulation results of an optical trapping concept,
in which a silicon nano-antenna produces a trapping potential for atoms in a
chip-scale configuration. Using counter-propagating incident fields,
bichromatically detuned from the atomic cesium D-lines, we numerically
investigate the dependence of the optical potential on the nano-antenna
geometry. We tailor the near-field potential landscape by tuning the evanescent
field of the waveguide using a toroidal nano-antenna, a configuration that
enables trapping of ultracold Cs atoms
Optical Pulling and Pushing Forces via Bloch Surface Waves
Versatile manipulation of nano- and microobjects underlies the optomechanics
and a variety of its applications in biology, medicine, and lab-on-a-chip
platforms. For flexible tailoring optical forces, as well as for extraordinary
optomechanical effects, additional degrees of freedom should be introduced into
the system. Here, we demonstrate that photonic crystals provide a flexible
platform for nanoparticles optical manipulation due to both Bloch surface waves
(BSWs) and the complex character of the reflection coefficient paving a way for
complex optomechanical interactions control. We demonstrate that appearance of
enhanced pulling and pushing transversal optical forces acting on a single bead
placed above a one-dimensional photonic crystal due to directional excitation
of Bloch surface wave at the photonic crystal interface. Our theoretical
results, which are supported with numerical simulations, demonstrate angle or
wavelength assisted switching between BSW-induced optical pulling and pushing
forces. Easy-to-fabricate for any desired spectral range photonic crystals are
shown to be prospective for precise optical sorting of nanoparticles,
especially for core-shell nanoparticles, which are difficult to sort with
conventional optomechanical methods. Our approach opens opportunities for novel
optical manipulation schemes and platforms and enhanced light-matter
interaction in optical trapping setups
Scattering Suppression from Arbitrary Objects in Spatially-Dispersive Layered Metamaterials
Concealing objects by making them invisible to an external electromagnetic
probe is coined by the term cloaking. Cloaking devices, having numerous
potential applications, are still face challenges in realization, especially in
the visible spectral range. In particular, inherent losses and extreme
parameters of metamaterials required for the cloak implementation are the
limiting factors. Here, we numerically demonstrate nearly perfect suppression
of scattering from arbitrary shaped objects in spatially dispersive
metamaterial acting as an alignment-free concealing cover. We consider a
realization of a metamaterial as a metal-dielectric multilayer and demonstrate
suppression of scattering from an arbitrary object in forward and backward
directions with perfectly preserved wavefronts and less than 10% absolute
intensity change, despite spatial dispersion effects present in the composite
metamaterial. Beyond the usual scattering suppression applications, the
proposed configuration may serve as a simple realisation of scattering-free
detectors and sensors
Invisibility and perfect absorption of all-dielectric metasurfaces originated from the transverse Kerker effect
Dielectric metasurfaces perform unique photonics effects and serve as the
engine of nowadays light-matter technologies. Here, we suggest theoretically
and demonstrate experimentally the realization of a high transparency effect in
a novel type of all-dielectric metasurface, where each constituting meta-atom
of the lattice presents the so-called transverse Kerker effect. In contrast to
Huygens' metasurfaces, both phase and amplitude of the incoming wave remain
unperturbed at the resonant frequency and, consequently, our metasurface
totally operates in the invisibility regime. We prove experimentally, for the
microwave frequency range, that both phase and amplitude of the transmitted
wave from the metasurface remain almost unaffected. Finally, we demonstrate
both numerically and experimentally and explain theoretically in detail a novel
mechanism to achieve perfect absorption of the incident light enabled by the
resonant response of the dielectric metasurfaces placed in the vicinity of a
conducting substrate. In the subdiffractive limit, we show the aforementioned
effects are mainly determined by the optical response of the constituting
meta-atoms rather than the collective lattice contributions. With the spectrum
scalability, our findings can be incorporated in engineering devices for energy
harvesting, nonlinear phenomena and filters applications.Comment: 10 pages, 6 figure
Magnetic field concentration with coaxial silicon nanocylinders in the optical spectral range
Resonant magnetic energy accumulation is theoretically investigated in the optical and near-infrared regions. It is demonstrated that the silicon nanocylinders with and without coaxial through holes can be used for the control and manipulation of optical magnetic fields, providing up to 26-fold enhancement of these fields for the considered system. Magnetic field distributions and dependence on the parameters of nanocylinders are revealed at the wavelengths of magnetic dipole and quadrupole resonances responsible for the enhancement. The obtained results can be applied, for example, to designing nanoantennas for the detection of atoms with magnetic optical transitions
Magnetoelectric Exceptional Points in Isolated All-Dielectric Nanoparticles
We consider the scattering of electromagnetic waves by non-spherical
dielectric resonators and reveal that it can be linked to the exceptional
points underpinned by the physics of non-Hermitian systems. We demonstrate how
symmetry breaking in the shape of an isolated dielectric nanoparticle can be
associated with the existence of an exceptional point in the eigenvalue
spectrum and formulate the general conditions for the strong coupling of
resonances, illustrating them for the example of the electric dipole and
magnetic dipole modes supported by a silicon nanoparticle. We argue that any
two modes of a dielectric nanoparticle can lead to an exceptional point
provided their resonant frequencies cross as a function of a tuning parameter,
such as, e.g. its aspect ratio, and their field distributions should have
opposite signs after a reflection in the transverse plane of the structure. The
coupled modes radiate as a mixture of electric and magnetic dipoles, which
result in a strong magnetoelectric response, being easily controlled by the
symmetry breaking perturbation. We also investigate the influence of a
dielectric substrate, demonstrating how the latter provides an additional
mechanism to tune the position of exceptional points in the parameter space.
Finally, we discuss applications of magnetoelectric exceptional points for
refractive index sensing
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