Concentration Of Electromagnetic Energy Research Articles

Influence of Spatial Dispersion on the Electromagnetic Properties of Magnetoplasmonic Nanostructures.

Magnetoplasmonics based on composite nanostructures is widely used in many biomedical applications. Nanostructures, consisting of a magnetic core and a gold shell, exhibit plasmonic properties, that allow the concentration of electromagnetic energy in ultra-small volumes when used, for example, in imaging and therapy. Magnetoplasmonic nanostructures have become an indispensable tool in nanomedicine. The gold shell protects the core from oxidation and corrosion, providing a biocompatible platform for tumor imaging and cancer treatment. By adjusting the size of the core and the shell thickness, the maximum energy concentration can be shifted from the ultraviolet to the near infrared, where the depth of light penetration is maximum due to low scattering and absorption by tissues. A decrease in the thickness of the gold shell to several nanometers leads to the appearance of the quantum effect of spatial dispersion in the metal. The presence of the quantum effect can cause both a significant decrease in the level of energy concentration by plasmon particles and a shift of the maxima to the short-wavelength region, thereby reducing the expected therapeutic effect. In this study, to describe the influence of the quantum effect of spatial dispersion, we used the discrete sources method, which incorporates the generalized non-local optical response theory. This approach made it possible to account for the influence of the nonlocal effect on the optical properties of composite nanoparticles, including the impact of the asymmetry of the core-shell structure on the energy characteristics. It was found that taking spatial dispersion into account leads to a decrease in the maximum value of the concentration of electromagnetic energy up to 25%, while the blue shift can reach 15 nm.

Single-nanoantenna driven nanoscale control of the VO2 insulator to metal transition

Abstract The ultrafast concentration of electromagnetic energy in nanoscale volumes is one of the key features of optical nanoantennas illuminated at their surface plasmon resonances. Here, we drive the insulator to metal phase transition in vanadium dioxide (VO2) using a laser-induced pumping effect obtained by positioning a single gold nanoantenna in proximity to a VO2 thermochromic material. We explore how the geometry of the single nanoantenna affects the size and permittivity of the nanometer-scale VO2 regions featuring phase transition under different pumping conditions. The results reveal that a higher VO2 phase transition effect is obtained for pumping of the longitudinal or transversal localized surface plasmon depending on the antenna length. This characterization is of paramount importance since the single nanoantennas are the building blocks of many plasmonic nanosystems. Finally, we demonstrate the picosecond dynamics of the VO2 phase transition characterizing this system, useful for the realization of fast nano-switches. Our work shows that it is possible to miniaturize the hybrid plasmonic-VO2 system down to the single-antenna level, still maintaining a controllable behavior, fast picosecond dynamics, and the features characterizing its optical and thermal response.

Coherent Networks of Si Nanocrystals: Tunable Collective Resonances with Narrow Spectral Widths

The ultralong coherent networks of Si nanocrystals (NCs) via lattice‐enhanced dipole–dipole coupling and the formation of disordered arrays of phase‐correlated field hotspots are studied. Such arrays occur in structures consisting of Si NCs randomly positioned inside long strips that are periodically repeated. The theoretical results predict the formation of all‐dielectric coherent networks of Si NCs, formed via in‐phase coupling of the resonances generated by diffraction of light. Such networks are extended along the lengths of the strips while supporting high field enhancement associated with the phase‐correlated chains of field hotspots between the nanocrystals. It is shown that these phenomena occur at the wavelengths where the Rayleigh anomaly condition is satisfied. Under this condition the electric field is squeezed between two field‐impenetrable regions, causing efficient concentration of electromagnetic energy along the disordered arrays of Si NCs in each strip. The results show that these arrays act as coherently assembled units that are efficiently coupled with the lattice modes, forming highly tunable collective resonances with spectral widths less than 5 nm. These results pave the way for all‐dielectric‐tunable optical filters with very small losses and near‐perfect reflectivity and laser systems based on Si NCs.

Breaking plasmonic symmetry through the asymmetric growth of gold nanorods

The optoelectronic properties of asymmetric metal nanostructures are of current interest for applications in photonics, sensing, and catalysis. Here, we break the symmetry of the localized surface plasmon resonance of gold nanorods by selective overgrowth of a single tip via a high-yield ( > --> 80 % ) wet-chemical method. While optical spectroscopy exhibits a bathochromic shift of the nanoparticle plasmon resonance, cathodoluminescence and electron energy loss spectroscopy measurements reveal a breaking of the symmetry of the associated localized surface plasmon resonance mode, which results in the subwavelength concentration of electromagnetic energy. The simple, one-step postsynthetic modification allows control of nanoparticle structural parameters, and we demonstrate how the asymmetric energy redistribution leads to increases in the surface-enhanced Raman scattering of a model analyte attached to the surface of the nanostructures. The spatial localization of energy in these nanostructures may find applications in nanofocusing, nanoimaging, and light harvesting.

Omnidirectional Surface Plasmon Polaritons Concentration in 3D Metallic Structures

3D metallic structures with symmetrically curved surfaces are proposed for surface plasmon polaritons (SPPs) deflection and concentration. Two-photon polymerization (2PP) and a sputtering process are applied for the preparation of the proposed structures. Leakage radiation microscopy (LRM) is used for the excitation and observation of SPPs. The characterization results reveal that the proposed structures are able to deflect SPPs and partly concentrate SPPs energy when the surface waves propagate around the raised part of the metallic structure. The maximum electromagnetic energy concentration can be reached when SPPs propagate towards the center of the raised part of the structure. An investigation on the energy concentration performance of the proposed metallic structures with respect to different profiles is analytically and experimentally carried out. Applications of plasmonic devices for energy harvesting elements, omnidirectional light absorbers, and benders are discussed.

All-dielectric concentration of electromagnetic fields at the nanoscale: the role of photonic nanojets.

The photonic nanojet (PNJ) is a narrow high-energy beam that was originally found on the back side of all-dielectric spherical structures. It is a unique type of energy concentration mode. The field of PNJs has experienced rapid growth in the past decade: nonspherical and even pixelized PNJ generators based on new physics and principles along with extended photonic applications from linear optics to nonlinear optics have driven the re-evaluation of the role of PNJs in optics and photonics. In this article, we give a comprehensive review for the emerging sub-topics in the past decade with a focus on two specific areas: (1) PNJ generators based on natural materials, artificial materials and nanostructures, and even programmable systems instead of conventional dielectric geometries such as microspheres, cubes, and trihedral prisms, and (2) the emerging novel applications in both linear and nonlinear optics that are built upon the specific features of PNJs. The extraordinary features of PNJs including subwavelength concentration of electromagnetic energy, high intensity focusing spot, and lower Joule heating as compared to plasmonic resonance systems, have made PNJs attractive to diverse fields spanning from optical imaging, nanofabrication, and integrated photonics to biosensing, optical tweezers, and disease diagnosis.

Side scattering shadow and energy concentration effects of epsilon-near-zero media.

By analytically and numerically investigating the near-field scattering properties of particles composed of epsilon-near-zero (ENZ) media, we reveal a unique scattering phenomenon which is hereby denoted as the side scattering shadow and energy concentration effect. The scattering of ENZ particles leads to the emergence of near-field "shadows," where the electric fields are significantly decreased to zero on two sides of the particle perpendicular to the incident direction. At the same time, the electric fields inside the particle are enhanced to a certain extent, indicating concentration of wave energy. These extraordinary behaviors can be well explained through the Mie scattering theory. Moreover, such unique effects robustly exist for isotropic and anisotropic ENZ particles of almost arbitrary shapes and with loss. We further demonstrate interesting applications of this effect, including the "quenching" of surface plasmons and the concentration of electromagnetic energy in the deep subwavelength scale. Our findings may inspire novel applications in nanophotonics.

Elucidating heterogeneity in nanoplasmonic structures using nonlinear photon localization microscopy

Using nonperturbative photon localization microscopy and electromagnetic simulation, it is observed that localized modes in plasmonic devices are significantly impacted by small, and frequently time-dependent, structural variations on the nanometer scale. This is important because many such devices rely on the concentration of electromagnetic energy at the ∼10 nm length scale and below for applications ranging from ultrasensitive molecular spectroscopy and detection, to chemical nano-imaging and plasmo-catalysis. In all devices, but particularly those based on noble metals, structural heterogeneity at these length scales is unavoidable, emphasizing the need for characterizing and understanding its effects. By exploiting the two-photon photoluminescence signal, one addresses the specific challenge of probing local electromagnetic fields inside the metal, which directly determine hot carrier generation and photoemission. It is found that heterogeneous nanoscale asperities serve as energy localization centers, and that functional impact is influenced primarily by two factors: position relative to a plasmonic mode volume, and how the asperity affects the smallest critical dimension, such as the size of a nanogap, in the structure.

Technique for Analysis of the Spatial Field Distribution in Tapered Wire Medium

The paper is devoted to experimental investigation of the spatial distribution of electromagnetic field in the vicinity of the tapered wire medium formed by copper wires conductors in the millimeter waveband. The experimental technique, based on the small perturbations method and used the special software has been elaborated for electromagnetic field distribution registering. The optimal type of probe has been determined. The electromagnetic energy concentration in the vicinity of the narrow planes of the tapered wire medium has been demonstrated experimentally. It is shown that the width of the wave beam behind the narrow facet of the lens insignificantly increases with distance. The field patterns with resolution ± 0.01dB in the vicinity of wide planes of lens have been registered.

Localized Temperature Stability in Low‐Temperature Cofired Ceramics

Low‐temperature cofired ceramic (LTCC) is a multilayer 3D packaging, interconnection, and integration technology. For LTCC modules targeting radio and microwave frequency (RF and MW) applications, a low or near 0 ppm/°C temperature coefficient of resonant frequency (τf) ensures temperature stability of embedded resonator and filter functions. The base dielectrics of most commercial LTCC systems have a τf in the range −50 to −80 ppm/°C. This study explored a method to achieve a zero τf on stripline (SL) resonators by locally cofiring, in a multilayer LTCC structure, compensating dielectrics (CD) with an opposite τf to that of the host dielectric. The formulation, synthesis, dielectric properties, and microstructure of SrTiO3 (STO)‐based low‐fire τf CD are presented. Chemical interactions and physical compatibility between the compensating and the host LTCC dielectrics are investigated for cofireability. The dependence of τf compensation on the wt% of STO, the printed thickness, and the location of the CD in multilayer LTCC are discussed. The most effective τf compensation is achieved by integrating CD next to the resonator lines, and can be explained by the concentration of electromagnetic energy via total internal reflection of electromagnetic waves inside the CD layer.

TIME-DELAY-BASED MULTI-TARGET DETECTION AND POWER DELIVERING

The paper presents an approach to locate and concentrate electromagnetic energy on targets based on time delays. An array of antennas is used in the approach, in which one antenna sends ultra- wide-band signals, and all antennas receive the signals backscattered by the targets. The time delays can be obtained by the interrelation of the transmitted and received signals. By controlling the timing of the pulses radiated from the individual antennas, high concentration of electromagnetic energy on the targets' locations can be achieved. The performance of this approach is demonstrated by several numerical simulations.

Nanofocusing of Surface Plasmon Polaritons by the Tapered Metallic Plasmonic Waveguide: Optimal Angle Near the Apex

Conditions for the optimal concentration of electromagnetic energy of the optical frequency at the apex of the sharp tapered metallic tips used as the surface plasmon polariton waveguide are considered. It is theoretically predicted that nanofocusing of the surface wave is optimal when singularity of the electric field of the focusing wave exists at the ideally sharp apex of the tip. For a given angle near the apex of the conical tip the frequency range, in which singularity of focused electric field exists in the vicinity of geometrically ideal apex, is found. The character of this singularity is analyzed. Analogously, for a given frequency of the surface plasmon polaritons the range of angles for which singularity of electric field exists at the tip’s apex is found.

Strongly Interacting Plasmon Nanoparticle Pairs: From Dipole−Dipole Interaction to Conductively Coupled Regime

We have investigated the optical response of periodic arrays of metallic (gold) nanoparticles composed of a pair of particles on each lattice site. By varying the interparticle separation within the pairs from dielectric proximity to conductive contact on a nanometer scale, we observe an abrupt, large renormalization as well as a splitting of the surface plasmon polariton energy. These spectral anomalies are ascribed to a transition whereupon the interparticle dipole−dipole interaction is shunted and the plasmon polaritons exhibit multipolar behavior, including a very high local concentration of electromagnetic energy in the vicinity of their conductive contact.

Resonant electromagnetism in photonic crystals composed of triangular-arrayed rods with both dielectric constant and magnetic permeability functions

The modified frequency-domain method was used to simulate the photonic properties of triangular-arrayed rods surrounded by air and possessing nonunity dielectric and magnetic permeability functions. It was found that the photonic bandgap becomes broader for the TE mode when material with higher magnetic permeability and lower dielectric constant is used for rods as compared with that of purely dielectric rods with the same refractive index, whereas the gap is reduced for the TM mode. We further examined the photonic characteristics of the photonic-crystal cavity formed when a point defect is introduced into the rod array. With a fixed refractive index of the rods, the resonant frequency of the TE mode in the first band gap is lower and the electromagnetic energy concentration at the point defect is higher when material with higher magnetic permeability and lower dielectric constant is used for the rods. The opposite was found for the TM mode.

A transient array to increase the peak power delivered to a localized region in space: part I-theory and modeling

It is shown that an array of pulsed antennas (a transient array) can be used for providing a high concentration of electromagnetic energy into small regions. By controlling the timing of the pulses radiated from the individual elements, selected regions of space will see a coherent superposition of the radiated pulses forming "hot spots." The formation of "hot spots" is demonstrated by theoretical analysis. Using a highly damped sinusoid for the radiated pulse and dipole antenna elements, a contour plot of the peak electric field is determined for a linear array of six equally spaced sources. The impact of pulse-timing errors and the factors determining the size of the hot spot are also considered.

Trapping of an electromagnetic wave by the boundary of created plasma

We discuss a new phenomenon of the electrodynamics of transient media, the trapping of electromagnetic radiation by the boundary of a transient plasma due to the conversion of the radiation into surface waves localized at the boundary. Calculations are done for an initial plane wave and for a beam of finite width in conditions where the boundary of the suddenly created (because of ionization) plasma half-space is perpendicular to the initial wavefront. Two frequency down-shifted surface waves traveling along the boundary in opposite directions are shown to be excited, as well as frequency up-shifted outgoing radiation and a time-independent mode in the form of a spatially inhomogeneous structure of dc currents and a magnetic field within the plasma half-space. We study the associated kinematic, amplitude, and energy relations. Finally, we establish that the most efficient trapping (up to 40% in energy) can be achieved with the forward (with respect to the direction of the initial wave propagation) surface mode and that the trapping is accompanied by concentration of electromagnetic energy at the plasma boundary.

Analysis of a hyperthermic treatment using a reentrant resonant cavity applicator for a heterogeneous model with blood flow

Hyperthermic treatment using a reentrant resonant cavity applicator is investigated. By solving time-dependent electromagnetic field-heat transfer equations for a heterogeneous model, temperature distributions in various organs are obtained. Calculated results show that it is indispensable to consider the blood flow to predict accurate temperature distributions during a hyperthermic treatment. Also, it is found that the necessity of measuring the electrical and thermal properties of the abdominal fat accurately as well as optimizing the heating system to avoid the concentration of electromagnetic energy around the abdominal fat-muscle interface.

A micro Z-pinch as a spark of an axial detonation

In order that a Z-pinch in a DT plasma could spark off an axial nuclear detonation wave severe conditions on space and time concentration of electromagnetic energy must be satisfied. Such energy compression could be achieved by a magnetic-field compressor (MFC) in which a fast liner compresses an azimuthal field (B φ) of a micro Z-pinch. The driver of the MFC could be either a heavy-ion beam or an explosive magnetic-field generator (EMG) destroyed at each shot. In conclusion, some of the major problems associated with this approach to ICF are outlined.

Electrodeless discharges and some allied problems

Electrodeless discharges in high-frequency electromagnetic fields were investigated in conditions where the ratio of linear dimension l of the discharge space to the electromagnetic wavelength λ in air was 10−3<l/λ<10−1, at frequencies between 106 and 108c/s. The power introduced into the discharge space varied from fractions of watts to 100 kW, and the electric field strength was varied between tens and hundreds of volts per cm. There are two different types of discharge: “E-discharges,” in which the elementary conductance currents are continued by dielectric currents, and “H-discharges,” with elementary conductance currents in the form of closed curves.When the ratio l/λ is less than 10−1 then the electrodeless discharges in air at atmospheric pressure may exist at distances of the order of centimetres from the current-carrying electrodes. Further development of the ultra-high-frequency technique leads to constructions of electromagnetic radiators in which the dimension l is greater than the wavelength λ. With such radiators it is possible to have high concentration of electromagnetic energy at distances x up to l2/λ which may be some metres or perhaps kilometres from the electromagnetic radiator. When 1 ≫ λ and l2≫ xλ it is possible for a natural breakdown to occur in an electromagnetic ray.