Evanescent Electromagnetic Waves Research Articles

Dynamic control of optical skyrmions in cylindrical waveguide

In recent times, the optical skyrmions have received an increasing amount of interest owing to its applications in optical manipulation, super-resolution imaging and microscopy, quantum technologies. However, few studies are focused on the dynamic control of optical skyrmions. It is found that Neel-type photonic skyrmions were discovered in evanescent electromagnetic waves. Here, we find the Bloch-type skyrmions in a three-dimensional cylindrical waveguide. By modulating the amplitude ratio of two incident vortex beams, the new types of skyrmions such as Twisted-type skyrmions and Planar-type skyrmions can be found. Further more, we have also achieved arbitrary modulation ratios of internal spin components. It is believed that our findings greatly enrich the types of photonic skyrmions and provide a method to freely control the photonic skyrmions.

Numerical Simulation of Electromagnetic Responses to an Earthquake Source Due To the Piezoelectric Effect of ‘∞m’ Symmetry

AbstractIt is reported that earthquakes are accompanied by electromagnetic (EM) anomalies. These anomalies are thought to be caused by earthquakes but their generation mechanism is still unclear. The piezoelectric effect has been proposed as a possible mechanism, particularly in quartz‐rich rocks. However, the EM responses to earthquakes due to such an effect have not been well understood. In this article, we study the EM signals generated by an earthquake source due to the piezoelectric effect. We develop a semi‐analytical method to simulate the EM responses to earthquake sources in a 3‐D layered model and conduct numerical simulations to investigate the characteristics of the EM fields. The results show that the piezoelectric effect in quartz‐rich rocks could be the responsible mechanism for the EM signals recorded during the earthquake. Two kinds of EM signals can be generated by the earthquake, namely, the early EM wave arriving before the seismic waves and the coseismic EM field accompanying the seismic waves. For an Mw 6.1 earthquake, the coseismic electric field is ∼0.1 μV/m and the magnetic field can only reach ∼10−5 nT. We also study the sensitivity of the coseismic EM fields to the rock conductivity. The results indicate that the coseismic EM fields are mainly affected by the conductivity of the shallow layer where the receiver is located, and if the top layer is thin, they are also affected by the conductivity of the deeper layer due to the contribution of the evanescent EM wave created at the interface.

Long-range polaritonic heat conduction in asymmetric surrounding media

Surface Phonon Polaritons (SPhPs) as an evanescent electromagnetic surface wave supports long propagation which readily surpasses the mean free path of classical heat carriers, e.g., phonons and electrons in solids. SPhPs have emerged as a promising candidate to dominate heat transfer in thin films. Polaritonic heat transfer has two distinct advantages: superior thermal conduction and a wide range of manipulation. Here, we study the upper limit of the thermal conductivity mediated by long-range polaritons in asymmetric surrounding media, where its surface effect overwhelms the volumetric one. The thin film structure strengthens the interactions of two surface waves at the top and bottom surfaces, and the asymmetric surrounding media makes an evanescent surface wave to further penetrate the free space with a higher refractive index, but it requires a fine tuning of asymmetric permittivity of the surrounding media to reach the upper limit of energy transmission efficiency near to the modal cut-off, where the transverse wavevector becomes zero. Both analytical and numerical simulations were introduced to investigate dispersion in asymmetric surrounding media and to model the thermal conductivity of glass thin films. Anomalously high thermal conductivity of 248 W/m-K was achieved with a 50 nm thick SiO2 film in asymmetric surrounding media, yet subtly dissimilar.

Arbitrary Polarization Syntheses Based on Spin‐Momentum Locking in Spoof Surface Plasmon Polaritons

AbstractSpin‐momentum locking is universal and an inherent property of evanescent electromagnetic (EM) waves, which transfers the spinning or handedness of electromagnetic waves onto their propagation direction. This motivates an approach to investigate the polarization‐controlled directional transmission or emission. Here, the spin‐momentum locking is demonstrated in spoof surface plasmon polariton (SSPP) waveguides, and momentum‐controlled radiation is further realized in SSPP‐patch antennas. The study shows that the circular polarization of the SSPP‐patch antennas originates from the spin‐momentum locking in the SSPP waveguides and hence is determined by the propagation direction of the SSPP modes. Two examples are presented to achieve ±45° dual‐polarizations and vertical/horizontal dual‐polarizations by combining the SSPP‐patch antenna with hybrid couplers. Finally, a straightforward method is proposed for synthesizing the polarization emitted by the SSPP‐patch antenna, allowing access to arbitrary polarization states on the Poincare sphere. The SSPP‐patch antenna is polarization responsive, shedding light on chiral sensors, Stokes polarimetry, and polarization measurement. Hence, the spin‐momentum locking and the related momentum‐controlled radiations provide additional freedom to regulate the EM waves by engineering the helicity in the SSPP waveguide.

Characteristics of surface plasmonic modes in cylindrical chiral-graphene-dielectric waveguide structure

A cylindrical chiral-graphene-dielectric waveguide structure is proposed. Correspondingly, characteristics of surface plasmonic mode are theoretically investigated, including dispersion relation, intensity, phase and polarization distribution. The proposed waveguide can only support the vortex modes with the hybrid polarization distribution, which originates from the spin-momentum locking of evanescent electromagnetic waves. The circular birefringence of chiral materials releases the degeneracy between same-order vortex modes. In addition, the number of modes can be controlled by changing the radius of the dielectric nanowire and the Fermi level of graphene. The effective index and corresponding propagation length of the mode are sensitive to the chiral parameter. We believe the proposed waveguide can find some potential applications in multiplex communication, chiral sensing and the fabrication of tunable nano-photonic devices.

Propagation of visible light in nanostructured niobium stripes embedded in a dielectric polymer

Abstract Nanometric metallic stripes allow the transmission of optical signals via the excitation and propagation of surface-localized evanescent electromagnetic waves, with important applications in the field of nano-photonics. Whereas this kind of plasmonic phenomena typically exploits noble metals, like Ag or Au, other materials can exhibit viable light-transport efficiency. In this work, we demonstrate the transport of visible light in nanometric niobium stripes coupled with a dielectric polymeric layer, exploiting the remotely-excited/detected Raman signal of black phosphorus (bP) as the probe. The light-transport mechanism is ascribed to the generation of surface plasmon polaritons at the Nb/polymer interface. The propagation length is limited due to the lossy nature of niobium in the optical range, but this material may allow the exploitation of specific functionalities that are absent in noble-metal counterparts.

Transition from surface phonon-polariton to surface phonon–plasmon-polariton by thermal injection of free carriers

Surface phonon-polariton, surface plasmon-polariton, and surface phonon–plasmon-polariton are evanescent electromagnetic waves confined to the surfaces of different classes of materials, which gives each of them particular characteristics suitable for diverse applications. Natural or forced injection of free carriers in a dielectric may change the surface phonon-polariton into a surface phonon–plasmon-polariton. Understanding this effect provides an insight into the fundamental physics of surface electromagnetic waves on dielectrics and offers tools that can be used to develop new technologies. In this contribution, we experimentally study the transition from surface phonon-polariton to surface phonon–plasmon-polariton on a yttrium-doped aluminum nitride polycrystalline substrate by thermal injection of free carriers. We perform this study using reflectivity measurements in the far- and mid-infrared spectral range and at a variable temperature, taking the necessary precautions to eliminate any errors that may arise from measurement artifacts and inaccurate analysis of the spectra. We demonstrate that thermal injection of a significant free carrier density can tune the surface phonon-polariton into a much shorter mean free path surface phonon–plasmon-polariton.

Understanding energy propagation during reflection of an evanescent electromagnetic wave

Reflection of plane electromagnetic waves at a planar surface separating two media is typically discussed at length in undergraduate texts. However, a similar analysis for the case of evanescent electromagnetic waves, although illustrative and interesting, is rarely discussed. In this paper, we present such an analysis for the reflection of an evanescent wave at a plane dielectric surface and highlight the important conceptual difference in the energy flow for this case compared to that of a plane wave. It is generally emphasized that an evanescent wave does not propagate energy away from the surface emanating these waves. We show that in the case of an evanescent wave, the pair of incident and reflected waves together propagates energy if the imaginary part of the reflectivity is non-zero. Further, the real part of the reflectivity can be greater than unity in the case of an evanescent wave without violating energy conservation. Connection of these properties to the existence of surface modes, Čerenkov radiation, and a quantum analogue are elucidated in the paper.

Semi-analytical solutions of seismo-electromagnetic signals arising from the motional induction in 3-D multi-layered media: part II\u2014numerical investigations

In this paper, numerical computations are carried out to investigate the seismo-electromagnetic signals arising from the motional induction effect due to an earthquake source embedded in 3-D multi-layered media. First, our numerical computation approach that combines discrete wavenumber method, peak-trough averaging method, and point source stacking method is introduced in detail. The peak-trough averaging method helps overcome the slow convergence problem, which occurs when the source–receiver depth difference is small, allowing us to consider any focus depth. The point source stacking method is used to deal with a finite fault. Later, an excellent agreement between our method and the curvilinear grid finite-difference method for the seismic wave solutions is found, which to a certain degree verifies the validity of our method. Thereafter, numerical computation results of an air–solid two-layer model show that both a receiver below and another one above the ground surface will record electromagnetic (EM) signals showing up at the same time as seismic waves, that is, the so-called coseismic EM signals. These results suggest that the in-air coseismic magnetic signals reported previously, which were recorded by induction coils hung on trees, can be explained by the motional induction effect or maybe other seismo-electromagnetic coupling mechanisms. Further investigations of wave-field snapshots and theoretical analysis suggest that the seismic-to-EM conversion caused by the motional induction effect will give birth to evanescent EM waves when seismic waves arrive at an interface with an incident angle greater than the critical angle θc = arcsin(Vsei/Vem), where Vsei and Vem are seismic wave velocity and EM wave velocity, respectively. The computed EM signals in air are found to have an excellent agreement with the theoretically predicted amplitude decay characteristic for a single frequency and single wavenumber. The evanescent EM waves originating from a subsurface interface of conductivity contrast will contribute to the coseismic EM signals. Thus, the conductivity at depth will affect the coseismic EM signals recorded nearby the ground surface. Finally, a fault rupture spreading to the ground surface, an unexamined case in previous numerical computations of seismo-electromagnetic signals, is considered. The computation results once again indicate the motional induction effect can contribute to the coseismic EM signals.

Bloch-type photonic skyrmions in optical chiral multilayers

Magnetic skyrmions are topological quasiparticles in magnetization. Recently, as one of their photonic counterparts, Néel-type photonic skyrmions were discovered in evanescent electromagnetic waves. The deep-subwavelength features of the photonic skyrmions suggest their potential in optical imaging quantum technologies and data storage. Here, by exploiting the photonic quantum spin Hall effect of a plasmonic vortex in a trilayered structure, we predict the existence of photonic twisted-Néel- and Bloch-type skyrmions in chiral materials. Their chirality-dependent features can be considered as additional degrees of freedom for future chiral sensing, information processing, and storage technologies. In particular, our findings enrich the formations of photonic skyrmions and reveal a remarkable resemblance of the feature of chiral materials in two seemingly distant fields: photonic skyrmions and magnetic skyrmions.2 MoreReceived 16 December 2020Accepted 9 April 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.023109Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasChiralityLight-matter interactionNanophotonicsNear-field opticsPlasmonicsSkyrmionsTopological effects in photonic systemsAtomic, Molecular & Optical

The Influence of the Asymmetry of the Geometry of a Core–Shell Particle on a Substrate on the Optical Characteristics Accounting for Spatial Dispersion

The problem of excitation of a core–shell particle located on a transparent substrate by a field of an evanescent electromagnetic wave is considered. The particle consists of a dielectric core with a metal nanoplasmonic shell in which spatial dispersion occurs. Based on the Discrete Sources Method, a model has been constructed that considers the influence of the presence of the substrate and nonlocality in a metal on the optical scattering characteristics. The effect of the asymmetry of the particle geometry on the optical characteristics of the near field has been investigated. It was found that the asymmetry of the particle geometry significantly affects the intensity enhancement coefficient, as well as the absorption cross-section.

High Surface Phonon-Polariton in-Plane Thermal Conductance along Coupled Films.

Surface phonon-polaritons (SPhPs) are evanescent electromagnetic waves that can propagate distances orders of magnitude longer than the typical mean free paths of phonons and electrons. Therefore, they are expected to be powerful heat carriers capable of significantly enhancing the in-plane thermal conductance of polar nanostructures. In this work, we show that a SiO/Si (10 m thick)/SiO layered structure efficiently enhances the SPhP heat transport, such that its in-plane thermal conductance is ten times higher than the corresponding one of a single SiO film, due to the coupling of SPhPs propagating along both of its polar SiO nanolayers. The obtained results thus show that the proposed three-layer structure can outperform the in-plane thermal performance of a single suspended film while improving significantly its mechanical stability.

Momentum-Space Geometric Structure of Helical Evanescent Waves and Its Implications on Near-Field Directionality

In this paper, a momentum-space geometrical structure in helical evanescent electromagnetic waves is revealed. It is shown that for every helical evanescent wave on a helicity-dependent half tangent line in momentum space, the orientation of each of its field, spin, and Poynting vectors is the same. This geometric structure is revealed in a remarkable relation between the far-field and near-field components of the angular spectrum. Any general evanescent wave vector is linked to two points on the ${k}_{\ensuremath{\rho}}={k}_{0}$ circle of propagating wave vectors via two helicity-dependent tangent lines. Knowing the field of a general dipolar source on the ${k}_{\ensuremath{\rho}}={k}_{0}$ circle is sufficient to determine its entire evanescent angular spectrum. By applying this concept, we gain insights into near-field directionality by showing that every zero in the angular spectrum is a helicity singularity where two half tangent lines of opposite helicity intersect. A powerful method for the synthetic design of near-field directional sources is also devised, using structured helical illumination to gain full control of the near-field directionality. The results provide fundamental insight into helical evanescent waves and have implications in areas where chiral light-matter interaction plays a central role.

Numerical simulations to explain the coseismic electromagnetic signals: a case study for a M5.4 aftershock of the 2016 Kumamoto earthquake

Coseismic electromagnetic (EM) signals that appear from the P arrival were observed in a volcanic area during the 2016 Kumamoto earthquake. In this study, we conduct numerical simulations to explain the coseismic EM signals observed for a M5.4 aftershock of the earthquake. Initially, we adopt a water-saturated half-space model, and its simulation result for a receiver with a depth of 0.1 m suggests that the magnetic signals do not show up at the arrivals of P, refracted SV–P and Rayleigh waves because the evanescent EM waves just counterbalance the localized magnetic signals that accompany P, refracted SV–P and Rayleigh waves. Then, we conduct numerical simulations on a seven-layer half-space model in which the second layer corresponds to an aquifer analogy and the six other layers refer to air-saturated porous media. When only the electrokinetic effect is considered, the simulated coseismic magnetic signals still appear from the S arrival. The combination of electrokinetic effect and surface-charge assumption is also tested. We find that signals before the S arrival are missing on the transverse seismic, transverse electric, radial magnetic and vertical magnetic components, although the situation on horizontal magnetic components is improved to an extent. Then, we introduce an artificial scattering effect into our numerical simulations given that the scattering effect should exist in the volcanic area. New numerical result shows good agreement with the observation result on the signal appearance time. Hence, the combination of electrokinetic and scattering effects is a plausible explanation of coseismic EM signals. Further investigations indicate that coseismic electric and/or magnetic signals are more sensitive to the scattering effect and the aquifer thickness than seismic signals.

Radar pulses to image the subsurface using Ground Penetrating Radar (GPR)

Ground penetrating radar (GPR) is one of several non-destructive evaluation (NDE) methods for buried utilities that has been proposed and tested over the last couple of decades. This enables configuring a test system that can evaluate buried objects with a minimal disruption to environmental medium. Evanescent electromagnetic waves are inhomogeneous compounds of the near field, bound to the surface of the scattering object. These modes travel along the illuminated sample surface and exponentially decrease outside it, either in the form of lateral waves created by total internal reflection at dielectric flat interfaces and particles in metallic corrugated interfaces. One advantages of GPR is that it is able to analyze a buried object rapidly without having to contact the ground and measures the time interval between the generation of the impulse and its reception after the scattering, the results being presented in B-scan representation. This paper to present the results from a GPR survey at the scanning of a region containing a sewer pipe with unknown precise location that passes under a storage tank.

Combining TIR and FRET in Molecular Test Systems.

Pharmaceutical agents or drugs often have a pronounced impact on protein-protein interactions in cells, and in particular, cell membranes. Changes of molecular conformations as well as of intermolecular interactions may affect dipole-dipole interaction between chromophoric groups, which can be proven by measuring the Förster resonance energy transfer (FRET). If these chromophores are located within or in close proximity to the plasma membrane, they are excited preferentially by an evanescent electromagnetic wave upon total internal reflection (TIR) of an incident laser beam. For the TIR-FRET screening of larger cell collectives, we performed three separate steps: (1) setting up of a membrane associated test system for probing the interaction between the epidermal growth factor receptor (EGFR) and the growth factor receptor-bound protein 2; (2) use of the Epac-SH188 sensor for quantitative evaluation under the microscope; and (3) application of a TIR fluorescence reader to probe the interaction of GFP with Nile Red. In the first two steps, we measured FRET from cyan (CFP) to yellow fluorescent protein (YFP) by spectral analysis and fluorescence lifetime imaging (FLIM) upon illumination of whole cells (epi-illumination) as well as selective illumination of their plasma membranes by TIR. In particular, TIR excitation permitted FRET measurements with high sensitivity and low background. The Epac sensor showed a more rapid response to pharmaceutical agents, e.g., Forskolin or the A2B adenosine receptor agonist NECA, in close proximity to the plasma membrane compared to the cytosol. Finally, FRET from a membrane associated GFP to Nile Red was used to test a multi-well TIR fluorescence reader with simultaneous detection of a larger number of samples.

Transmission of Harmonic Signals Through a Wire Media

This paper is devoted to wire media (WM) investigation for signal transfer devices. Such devices are promising for different applications as imaging, power or signal transfer, sensing etc. However, first WMs could be used as a resonance structures, because the transfer of electromagnetic (EM) waves was possible only at the Fabry-Perot frequencies. It restricts the number of applications. However, the last works has shown the possibility of the broadband power transfer of evanescent electromagnetic waves. It allows using the same source of EM waves and their receiver to transfer the signals with different values of operation frequencies. Another investigation has proved that the WM does not distort the propagation wave. It allowed to suppose the possibility of pixel signal transfer that was studied in the paper and shown the ability of application of the such structures as the multichannel communication systems. With this aim the signals sources were allocated at the same plane with the input WM interface. First of all, the simulation investigations of the electric feld distributions of transferred harmonic signals through the WM have shown the needed period of dipoles allocations for the satisfactory resolution of received harmonic signals. One more conclusion from obtained results is the approvement that in this case the WM is not the resonance structure, but the same one operates with the signals of different frequencies. More detailed results and understanding of this were obtained from the spectrum analysis of the signals received at the output interface. It shown that the period of sources 2a is acceptable along x, y and diagonal directions. The spectrum analysis of the shape of the propagation wave also demonstrated and proven that the propagating signals do not suffer any nonlinear distortions. In the case of using of WM slab it can provide the excellent coupling between the interaction ports.

Lorentz-boosted evanescent waves

Polarization, spin, and helicity are important properties of electromagnetic waves. It is commonly believed that helicity is invariant under the Lorentz transformations. This is indeed so for plane waves and their localized superpositions. However, this is not the case for evanescent waves, which are well-defined only in a half-space, and are characterized by complex wave vectors. Here we describe transformations of evanescent electromagnetic waves and their polarization/spin/helicity properties under the Lorentz boosts along the three spatial directions.

Quantitative Understanding on the Amplitude Decay Characteristic of the Evanescent Electromagnetic Waves Generated by Seismoelectric Conversion

We conduct numerical simulations and theoretical analyses to quantitatively study the amplitude decay characteristic of the evanescent electromagnetic (EM) waves, which has been neglected in previous studies on the seismoelectric conversion occurring at a porous–porous interface. Time slice snapshots of seismic and EM wave-fields generated by a vertical single force point source in a two-layer porous model show that evanescent EM waves can be induced at a porous–porous interface. The seismic and EM wave-fields computed for a receiver array located in a vertical line nearby the interface are investigated in detail. In addition to the direct and interface-response radiation EM waves, we identify three groups of coseismic EM fields and evanescent EM waves associated with the direct P, refracted SV–P and direct SV waves, respectively. Thereafter, we derive the mathematical expression of the amplitude decay factor of the evanescent EM waves. This mathematical expression is further validated by our numerical simulations. It turns out the amplitude decay of the evanescent EM waves generated by seismoelectric conversion is greatly dependent on the horizontal wavenumber of seismic waves. It is also found the evanescent EM waves have a higher detectability at a lower frequency range. This work provides a better understanding on the EM wave-fields generated by seismoelectric conversion, which probably will help improve the interpretation of the seismoelectric coupling phenomena associated with natural earthquakes or possibly will inspire some new ideas on the application of the seismoelectric coupling effect.

Generation of interference patterns of evanescent electromagnetic waves at Fabry-Perot resonances of 1D photonic crystal modes

A diffractive structure for the generation of high-frequency interference patterns of evanescent electromagnetic waves based on the interference of the “volume” modes of 1D dielectric photonic crystal at Fabry-Perot resonances is proposed. The obtained results may find application in the design of novel devices for near-field interference photolithography.