Despite the apparent simplicity, the problem of refraction of electromagnetic waves at the planar interface between two media has an incredibly rich spectrum of unusual phenomena. An example is the paradox that occurs when an electromagnetic wave is incident on the interface between a hyperbolic medium and an isotropic dielectric. At certain orientations of the optical axis of the hyperbolic medium relative to the interface, the reflected wave is completely absent. In this paper, we formulate the aforementioned paradox and present its resolution by introduction of infinitesimal losses in a hyperbolic medium. We show that the reflected wave exists, but became extremely decaying as the loss parameter tends to zero. As a consequence, all the energy scattered into the reflected channel is absorbed at the interface. We support our reasoning with analytical calculations, numerical simulations, and an experiment with self-complementary metasurfaces in the microwave region.
We demonstrate that a hybrid c-Si/Au nanocavity can serve as a multifunctional sensing platform for nanoscale (about 100 nm) thermometry with high accuracy (>0.4 K) and fast response (<0.1 second), controlled local optical heating up to 1200 K and also provide Raman scattering enhancement (>10^4 fold). The system has been tested in the experiment on thermally induced unfolding of BSA molecules, plased inside the hybrid nanocavity. Moreover, numerical modeling reveal, that two possible operation modes of the system: with and without considerable optical heating at the nanometer scale, while other functionalities (nanothermometry, RS enhancement, and tracing the events) are preserved. These regimes make the hybrid nanocavity more versatile sensing system than fully plasmonic counterparts. The simplicity and multifunctionality of the hybrid nanocavity make it a promising platform for photochemistry and photophysics applications.
We study the scattering of light from homogeneous cylindrical objects embedded in a transparent and homo- geneous surrounding medium that is know as the Mie problem. We analyze Mie scattering by expansion of the scattering amplitude in the series near resonant frequency and find that Lorenz-Mie coefficient can be de- scribed by Fano formula, while both waves are involved in interaction completely and intensity vanishes at the special point of switching to the invisible regime. We analyze Fano interference between resonant wave and background in general case and discuss scattering-cancellation condition. We study the influence of the aspect ratio on the mode structure and find that Mie modes shift to the long wave lengths when the cylinder aspect ratio r/h decreases. Experimentally measured spectra in microwave range are in agreement with the theoretical predictions.
We introduce a concept of phase transitions between photonic crystals and all-dielectric metamaterials suggesting a phase diagram that places two classes of such artificial structures on a common parameter plane.1 We consider photonic crystals and all-dielectric metamaterials composed of the similar structural elements and arranged in the similar geometry of a two-dimensional (2D) square lattice of dielectric cylinders of large dielectric permittivity. Such structures can display negative magnetic permeability in the TE-polarization due to the Mie resonance that occurs below the lowest Bragg resonance.2 We define a point of transition from photonic crystals to all-dielectric metamaterials as a point when the lowest Mie resonance splits from the lowest Bragg resonance creating the lowest photonic gap. Based on the numerical results, we construct the phase diagram photonic crystals - all- dielectric metamaterials for the 2D square lattice of circular rods for the TE polarization. We have verified our theoretical concept experimentally by engineering a “metacrystal” composed of glass tubes filled with water forming a 2D square lattice with a variable lattice constant.
We review a new, rapidly developing field of all-dielectric nanophotonics which allows to control both magnetic and electric response of structured matter by engineering the Mie resonances in high-index dielectric nanoparticles. We discuss optical properties of such dielectric nanoparticles, methods of their fabrication, and also recent advances in all-dielectric metadevices including couple-resonator dielectric waveguides, nanoantennas, and metasurfaces.
KEYWORDS: Plasmonics, Near field optics, Near field scanning optical microscopy, Solar cells, Thin film solar cells, Silver, Metals, Electron beam lithography, Photovoltaics, Nanoantennas
Domino modes are highly-confined collectivemodes that were first predicted for a periodic arrangement of metallic
parallelepipeds in far-infrared region. The main feature of domino modes is the advantageous distribution of the
local electric field, which is concentrated between metallic elements (hot spots), while its penetration depth in
metal is much smaller than the skin-depth. Therefore, arrays of non-resonant plasmonic nanoantennas exhibiting
domino modes can be employed as broadband light trapping coatings for thin-film solar cells. However, until
now in the excitation of such modes was demonstrated only in numerical simulations. Here, we for the first
time demonstrate experimentally the excitation of optical domino modes in arrays of non-resonant plasmonic
nanoantennas. We characterize the nanoantenna arrays produced by means of electron beam lithography both
experimentally using an aperture-type near-field scanning optical microscope and numerically. The proof of
domino modes concept for plasmonic arrays of nanoantennas in the visible spectral region opens new pathways
for development of low-absorptive structures for effective focusing of light at the nanoscale.
We study the radiative decay and Purcell effect for finite-size electric and magnetic dipole emitters placed in an
uniaxial medium. For both electric and magnetic dipoles, we find that the radiative rate is strongly enhanced
in the hyperbolic regime, when the signs of the longitudinal and transverse dielectric constants are opposite.
However, the behavior of the Purcell factor in the transition region from elliptic to hyperbolic regimes is very
different for the electric and magnetic dipoles. The Purcell factor enhancement for magnetic dipole is weaker
and it takes place only deep inside the hyperbolic regime, while for electric dipole the maximum enhancement is
achieved at the transition boundary.
The study of optical nanoantennas is a rapidly developing area of optics and nanophotonics. Nowdays, the most popular type of nanoantennas is a plasmonic one made of metallic elements. However, plasmonic nanoantennas have large dissipative losses. Here we present an overview of the recent results of a newly emerged field of all-dielectric optical nanoantennas. These optical nanoantennas are made of high-permittivity low-loss dielectric particles. Moreover, in addition to the electric resonances such nanoscale particles exhibit very strong magnetic response in the visible range. We introduce and study a highly efficient Huygens element and Yagi-Uda type nanoantennas based on dielectric nanoparticles. We also introduce a novel concept of all-dielectric superdirective nanoantennas based on the generation of higher-order optically-induced magnetic multipole modes. For such superdirective dielectric nanoantennas, we predict the effect of beam steering at the nanoscale characterized by a subwavelength sensitivity of the beam radiation direction to the source position. Based on all these new properties, optical nanoantennas offer unique opportunities for applications such as optical communications, photovoltaics, non-classical light emission, and sensing.
We consider spatial hysteresis and modulational instability in arrays of nonlinear metallic nanoparticles. We show
that such plasmonic systems are characterized by a bistable response, and they can support the propagation of
dissipative switching waves (or plasmonic kinks) connecting the states with different polarization. We demonstrate
that modulational instability, also inherent in our system, can lead to the formation of regular periodic
or quasi-periodic modulations of the polarization. We reveal that arrays of metallic nanoparticles can support
nonlinear localized modes of two different types - plasmon-solitons and plasmon-oscillons. They both possess
deeply subwavelength size. However, the profile of plasmon-solitons is stationary; whereas plasmon-oscillons has
the oscillating profile which can stand at rest or slowly drift along the chain.
We analyzed capabilities and functionalities of a multisegment superlens recently suggested for long-distance transport of color images with subwavelength resolution. We studied the performance of three- and six-segment nanolens structures by analyzing numerically both transmission and reflection coefficients and by employing the full-wave simulations for a particular source arrangement. Our results suggest that such multisegment structures offer limited subwavelength imaging performance with a relatively narrow frequency band.
Tailoring the parameters of a silver nanorod array for subwavelength imaging of arbitrary coherent sources is of recent interest. We evaluated the operational bandwidth of this type of superlens, and also the impact of source-offset in order to understand the level of tolerance offered by the superlens with regard to source location. The performance of the device was analyzed numerically both through analysis of transmission and reflection coefficients and by full-wave simulation for a particular sample source arrangement. We observed that such a device exhibited better imaging performances with the sources spread wider, offering a bandwidth of around 13.5%.
Periodic layered metal-dielectric nanostructures are used in subwavelength imaging, invisibility cloaking, nano-lithography
and optical nanocircuitry. These optical metamaterials are usually described by local effective
medium model if their periods are much smaller than a wavelength. Our studies show that even under such
strict conditions the metamaterials are nonlocal and exhibit strong spatial dispersion effects. The uniaxial media
support two or more extraordinary waves in certain directions while the local effective model predicts only one.
The strong spatial dispersion is caused by surface plasmon polariton modes at the interfaces between metal and
dielectric layers.A
The material parameters of nano-fishnet optical metamaterials are evaluated numerically through
extraction from reflection and transmission coefficients of structures consisting of multiple nano-fishnet
pairs. For extraction the Nicholson-Ross-Weir method was modified. Effects of
convergence with increase of number layers are discussed. Bulk electrodynamics parameters of
the structure are discussed.
KEYWORDS: Imaging arrays, Coherence imaging, Silver, Near field scanning optical microscopy, Interfaces, Computer simulations, Metals, Near field optics, Near field, Nanorods
The arrays of silver nanorods are known as prospective structures for near-field transmission. However, the
available geometries are operating with incoherent sources and do not properly image the coherent ones. In this
paper it is demonstrated how the geometry proposed in [Phys. Rev. Lett. 95, 267407 (2005)] can be modified
to enable subwavelength imaging of arbitrary coherent sources. The greatly improved performance of the device
is demonstrated numerically both through analysis of transmission and reflection coefficients and by full-wave
simulation of a particular source imaging.
This paper presents an analytical theory describing excitation of a semi-infinite electromagnetic crystal by plane electromagnetic wave. A three-dimensional crystal with orthorhombic elementary cell, formed by scatterers which can be substituted by point dipoles with known polarizability and fixed orientation is considered. The closed-form analytical formulae for the amplitudes of excited modes and Floquet harmonics of scattered field for the semi-infinite electromagnetic crystal are derived in terms of the infinite crystal eigenmodes wavevectors. Generalized Ewald-Oseen extinction principle for electromagnetic crystals under consideration has been formulated.
It is extended for electromagnetic crystals of general kind characterized by three-periodical dielectric permittivity distribution.
Analytical theory of plane electromagnetic wave reflection from a layer or half-space of a particulate photonic crystal is introduced. The photonic (artificial) crystal is formed by small complex-shaped dielectric or metallic inclusions arranged in the nodes of a regular three-dimensional lattice with parallelepipedal elementary cell of general kind. The dipole model and the local-field approach are used for description of electromagnetic interaction between inclusions. Frequency-dependent polarizabilities are used for description of inclusions polarization. The interaction between adjacent layers is considered using the Floquet representation including evanescent modes. Using an analytical theory of dispersion for the crystals under consideration it becomes possible to make predictions for dipole moments distribution deep inside the layer. Additional corrections for distribution in the surface layers and amplitudes of predicted modes have been found numerically from a linear system of equation. This method needs much less computational time comparing with the same method without prediction of distribution and can be applied for calculation of reflection coefficient for much more thicker layers or for a half space. Also, a simple analytical single mode propagation theory for reflection from layer and half-space of particulate crystal is presented. It does not take into account the surface effects, but it is numerically shown for microwave crystal of loaded wires that this theory gives an excellent correspondence with exact one in the case of single mode propagation.
Recently, much attention has been paid to novel thin artificial impedance surfaces. For applications it is important that the thickness of the layer is as small as possible. One possible realization is based on the use of quasi-bulk cells, so that the resonance is achieved in thin layers due to concentration of the fields in equivalent capacitances and inductances. However, the geometry of these layers is quite complicated (3D cells), and it is not possible to increase the surface inductance keeping the thickness small. Another possible cause for resonance response can be near reactive fields generated at inhomogeneities or cracks. In this paper we investigate a doubly periodic array of small resonant scatterers positioned close to an ideally conducting plane. It is shown, that such a structure at the frequencies near the resonance acquires a very high impedance and behaves as magnetic screen.
Analytical theory of plane electromagnetic wave reflection from a layer or half-space of a particulate photonic crystal is introduced. The photonic (artificial) crystal is formed by small complex-shaped dielectric or metallic inclusions arranged in the nodes of a regular three-dimensional lattice with parallelepipedal elementary cell of general kind. The background medium is assumed to be an isotropic dielectric. The dipole model and the local field approach are used for description of electromagnetic interaction between inclusions. Frequency dependent polarizabilities are used for description of inclusions polarization. The interaction between adjacent layers is considered using the Floquet representation including evanescent modes. Using an analytical theory of dispersion for the crystals under consideration it becomes possible to make predictions for dipole moments distribution deep inside the layer. Additional corrections for distribution in the surface layers and amplitudes of predicted modes have been found numerically from a linear system of equation. This method needs much less computational time comparing with the same method without prediction of distribution and can be applied for calculation of reflection coefficient for much thicker layers or for a half space.
In this presentation we consider artificial (photonic) crystals formed by dielectric or metallic inclusions arranged in the nodes of a regular three-dimensional lattice with parallelepipedal elementary cell of the general kind. The background medium is an isotropic dielectric. Oblique propagation of plane electromagnetic waves in such a structure is under consideration. A simple analytical theory of plane-wave propagation which takes into account full-wave electromagnetic interactions of all inclusions is developed. The dipole model of interactions and the local- field approach are used. However, our interaction model takes into account the phase shift of the wave not only over a cell but also over the scatterer volume (using high-frequency polarizability). The layer- layer interactions are considered using the Floquet representation of the field produced by periodically polarized layers, including evanescent modes in the model of interactions of adjacent layers. The dispersion equation is obtained form the condition of polarization periodicity, which results from the geometry of the problem and solved numerically. As a simple illustrative example, numerical simulations for lattices of lossless dielectric spheres have been made. The present theory gives an analytical model for the effective propagation constant, which can be universally applied in a very wide frequency rage from the quasi-static regime to the Bragg reflection region (photonic band-gap).
The problem of electromagnetic mutual coupling of bianisotropic scatterers in the 3D regular arrays is considered. The arrays excited by a plane electromagnetic wave is assumed to be infinite in XY-coordinate plane and finite along OZ-axis, it is the lattice with rectangular cells. Each scatterer can be described as a couple of dipoles (electric and magnetic) having the arbitrary angle between them. The field interaction of these scatterers can be an important factor in the theory of bianisotropic composite media and also concerns the antenna array theory. A simple and rigorous model os such arrays is developed.
Regular 2D array of bianisotropic particles lying on a certain plane in free space is considered. The array (grid) is assumed to be infinite and the particles are small compared with the wavelength so that the dipole approximation is available. Here we use our recently developed theory of excitation of planar arrays of bianisotropic particles by plane waves. Both electric and magnetic moments of each particle are related between them and depend on the local field. Therefore the standard approach used in the theory of scanning antenna arrays cannot be applied. The analytical model allows to express the electric and magnetic moments induced in each particle through incident wave fields amplitudes. After calculating the electric and magnetic dipole moments induced in such an array by an incident plane wave we can evaluate the scattered fields. We calculate the reflection and transmission coefficients (which are dyadics) and analyze them.
A problem of electromagnetic interaction for 2D regular arrays of bianisotropic particles with rectangular cells is considered. They are excited by an incident plane electromagnetic wave. The local field in the point of location of an arbitrary chosen particle which can be named as reference-particle is formed by the incident wave and by field of all the particles besides reference-particle. Using dipole model we can express the local fields through only two vector complex values--electric and magnetic dipole moments of reference-particle. The relations between fields of other particles in the point of reference- particle location and dipole moments of the reference-particle are presented by several dyadics which are named as key dyadics. These dyadics play a very important role in solving of the problem of 2D and 3D regular grids excitation by an incident plane electromagnetic wave, because the equations relating electric and magnetic dipole moments of reference-particle with an incident wave field are presented through these dyadics and the polarizability ones. In this paper all components of key dyadics are exactly analytically calculated and their expressions are given in convenient for numerical calculations form.
The electromagnetic excitation of 2D array of bianisotropic particles by plane waves is considered. The array is assumed to be infinite and the particles to be small compared with the wavelength so that the dipole approximation is available. The electromagnetic interaction between tall the particles is taken into account analytically. Two kinds of bianisotropic particles: chiral particles and omega particles are analyzed. Both the electric and magnetic moments of each particle are related to each other and depend on the local field. Therefore, the standard approach used in the theory of scanning antenna arrays cannot be applied. The analytical model under consideration allows to express the electric and magnetic moments induced in each particle through incident wave field amplitudes. These relations are dyadic ones.
A problem of local field for 2D regular and weakly non- regular arrays of bi-anisotropic particles is considered. Such arrays are excited by an incident plane electromagnetic wave. The local field is formed by incident wave and by all the particles besides an arbitrary chosen particle under consideration which can be named as zero-particle. For infinite or very large arrays we can express the local fields with only tow vector complex values which are to be defined in frames of the separate problem of an exciting and scattering by such grids. But the equations relating electric and magnetic dipole moments of zero-particle with an incident wave field are that we find in this paper. Since these moments can be easily related with the surface density of electric and magnetic moments averaged on the grid surface the equations under consideration are analogues with the known local field formulae in theories of 3D media. Our relations are given by several dyadics which are named below as key dyadics.
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