Component Of Wave Vector Research Articles

Nonlinear Coupling of Kinetic Alfvén Waves and Ion Acoustic Waves in the Inner Heliosphere

We study the nonlinear coupling of kinetic Alfvén waves with ion acoustic waves applicable to the Earth’s radiation belt and near-Sun streamer belt solar wind using dynamical equations in the form of modified Zakharov systems. Numerical simulations show the formation of magnetic field filamentary structures associated with density humps and dips which become turbulent at later times, redistributing the energy to higher wavenumbers. The magnetic power spectra exhibit an inertial range Kolmogorov-like spectral index value of −5/3 for k ⊥ ρ i < 1, followed by a steeper dissipation range spectra with indices ∼ −3 for the radiation belt case and ∼ −4 for the near-Sun streamer belt solar wind case, here k ⊥ and ρ i represent the wavevector component perpendicular to the background magnetic field and the ion thermal gyroradius, respectively. Applying quasilinear theory in terms of the Fokker–Planck equation in the region of wavenumber turbulent spectra, we find the particle distribution function flattening in the superthermal tail population which is the signature of particle energization and plasma heating.

Phonon growth characteristics in one-dimensional cylindrical quantum wires at low lattice temperatures

The phonon growth characteristics in a cylindrical quantum wire structure has been theoretically analysed here under the condition of low lattice temperature. The present theory takes into account the effects of finite barrier height, energy band non-parabolicity of the material and the non-zero values of the transverse components of the phonon wave vector. At the low lattice temperatures again, the interaction of the non-equilibrium electrons with acoustic phonons becomes inelastic and consequently the phonon distribution cannot be approximated by the simple equipartition law. Hence the full form of the Bose-Einstein distribution for the phonon ensemble is taken into consideration. The numerical results that follow from the present theory for the wire samples of GaAs/Ga0.7Al0.3As and Ga0.47In0.53As/InP turn out to be quite different from what follows in the traditional simplified framework.

Realizing highly efficient vertical coupling with dielectric deflective metasurfaces.

Using dielectric deflective metasurfaces, we propose a novel, to the best of our knowledge, out-of-plane modulation scheme to realize vertical coupling on a 220 nm silicon-on-insulator platform. The metasurface is used to deflect vertical incident light to an oblique angle with high efficiency in the cladding layer. This deflection introduces a lateral wave vector component, thus preventing bi-directional transmission of traditional vertical coupling due to the second-order Bragg reflection of the grating. Additionally, an apodized design is employed for the subwavelength grating to improve mode matching with a deflection angle incident. The integration of the metasurface and subwavelength grating enables a new vertical coupling scheme with high efficiency. After global optimization, we achieved a simulation coupling efficiency of -2.19 dB. The measured coupling efficiency is -3.36 dB with a center wavelength of 1545.6 nm and a 1-dB bandwidth of 32 nm. The results confirm the feasibility of the proposed new architecture.

Non-reciprocity in photonic crystal due to parity time symmetric defect state

In this article, defect state of photonic crystal regarding parity time known as PT-symmetric is explored thoroughly. For this purpose, transfer matrix technique in setting Bloch theorem is employed to characterize the dispersion relation regarding PT-symmetric defect state. The study uncovers the norteworthy wave phenomenon entitle “non-reciprocity” is exhibited. Moreover, an increasing the in-plane component of wavevector contributes two or more branches in the short wavelength boundary of the stop-band which is not observed in conventional structures. The reflectance of structure is conducted across the optical regime leads to minimum point that aligns with the wavelength of the eigen mode for wavevector value (kx = 0). These findings of research may have significant applications in various areas of photonics and optics likes filters, modern optical photonic cavity resonators and thermo-photovoltaic devices etc.

Topological Phase Singularities in Light Reflection from Non‐Hermitian Uniaxial Media

AbstractPerfect light transmission into a dielectric at the Brewster angle is one of the simplest effects of macroscopic electromagnetism. The common wisdom states that absorption in the dielectric violates Brewster angle and leads to a non‐vanishing reflection. Yet, incorporating anisotropy may recover perfect transmission of p‐polarized light into the absorbing medium. Unlike the ordinary “lossless” Brewster angle, perfect transmission in this case is accompanied by phase singularities of the reflection amplitude. In this paper, phase singularities and the associated topological charges are theoretically examined as emerging in the wavelength‐incidence angle space upon perfect transmission into absorbing uniaxial dielectrics. The analytical criterion of perfect light transmission into an anisotropic medium is derived, phase singularities are demontrated in these scenarios, and their dynamics are studied as a function of material parameters. Finally, by lowering the symmetry of the problem, this phenomenon is translated into a different parameter space of wave vector components, and illustrate the feasibility of this phenomenon with available optically anisotropic materials. The results may become valuable for the development of novel analog computing schemes and holography approaches.

Revisiting physical mechanism of longitudinal photonic spin splitting and Goos-Hänchen shift

The intrinsic connection between the transverse photonic spin Hall effect (PSHE) and the Imbert–Fedorov shift has been well characterized. However, physical insights into the longitudinal photonic spin splitting associated with the Goos-Hänchen (GH) shift remain elusive. This paper aims to expand the theory of the PSHE generation mechanism from the transverse to the longitudinal case by examining the reflection of each spin component from an arbitrarily linearly polarized incident Gaussian beam on the air-dielectric interface. Unlike the transverse case, both spin-maintained and spin-flipped modes exhibit non-zero longitudinal displacements, with the latter being affected by the second-order expansion term of the Fresnel reflection coefficient with respect to the in-plane wave-vector component. Meanwhile, the polarization angle plays a crucial role in determining the longitudinal PSHE since each reflected total spin component is a coherent superposition of these two corresponding modes. Remarkably, the imaginary part of the relative permittivity of the dielectric significantly affects the symmetry of the longitudinal PSHE. Furthermore, the GH shift results from a superposition of individual spin states’ longitudinal displacements, taking into account their energy weights. By incorporating the corresponding extrinsic orbital angular momentum, we explore the generation mechanism of the symmetric/asymmetric longitudinal PSHE. The unified physical framework elucidating the longitudinal photonic spin splitting and GH shift provides a comprehensive understanding of the fundamental origin of the PSHE and beam shifts, paving the way for potential applications in spin-controlled nanophotonics.

Experimental investigation of a near-field focusing performance of the IP-Dip polymer based 2D and 3D Fresnel zone plate geometries fabricated using 3D laser lithography coated with hyperbolic dispersion surface layered metamaterial.

Herein we investigate the character of the near-field emission of a two- (2D) and novel three-dimensional (3D) probe geometries fabricated using 3D direct laser writing lithography. Near-field scans in x-y and y-z planes were measured both before and after the deposition of hyperbolic dispersion metamaterial (HMM) to further verify the directional propagation of the high wave-vector components present in the vicinity of the structures. Additional computational and theoretical characterization forewent the actual experimental measurements, showing a promising performance, particularly for the 3D Fresnel zone plate (FZP). Overall, the experimental data documents a subwavelength resolution with a significant signal enhancement in the focal spot of the 3D FZP and highly subwavelength depth of focus.

Evanescent modes in curved geometry

The evanescent modes' dependence on the topological properties of the surface over which optical fields propagate is examined. It is shown that curved geometries, unlike plane one, constrain the wave vector components to take discrete values. This implies that, for cylindrical surfaces, evanescent modes appear only in specific directions, while for spherical surfaces, they are forbidden. The limit of far-field is also investigated. These results are obtained using the angular spectrum technique and agree with the experimental results obtained by Raman scattering on tiny crystallites.

The propagation speed of optical speckle

That the speed of light in vacuum is constant is a cornerstone of modern physics. However, recent experiments have shown that when the light field is confined in the transverse plane, the observed propagation speed of the light is reduced. This effect is a consequence of the transverse structure which reduces the component of wavevector of the light in the direction of propagation, thereby modifying both the phase and group velocity. Here, we consider the case of optical speckle, which has a random transverse distribution and is ubiquitous with scales ranging from the microscopic to the astronomical. We numerically investigate the plane-to-plane propagation speed of the optical speckle by using the method of angular spectrum analysis. For a general diffuser with Gaussian scattering over an angular range of 5°, we calculate the slowing of the propagation speed of the optical speckle to be on the order of 1% of the free-space speed, resulting in a significantly higher temporal delay compared to the Bessel and Laguerre–Gaussian beams considered previously. Our results have implications for studying optical speckle in both laboratory and astronomical settings.

Lines of Quasi-BICs and Butterworth Line Shape in Stacked Resonant Gratings: Analytical Description

We propose analytical approximations of the reflection and transmission spectra of a stacked dielectric diffraction grating consisting of two identical resonant guided-mode gratings with a Lorentzian line shape. These approximations, derived using the scattering matrix formalism, are functions of both angular frequency ω and the tangential wave vector component kx of the incident wave. We analytically demonstrate and, using full-wave simulations with rigorous coupled-wave analysis technique, numerically confirm that by a proper choice of the thickness of the dielectric layer separating the gratings, one can tailor the resonant optical properties of the stacked structure. In particular, it is possible to obtain lines of quasi-bound states in the continuum in the ω–kx parameter space with the quality factor decaying proportionally to kx−4 or kx−6. In addition, the stacked structure can be used as a spectral or spatial Butterworth filter operating in reflection. The presented results may find application in the design of optical filters and sensors based on stacked resonant gratings.

In-Plane and Out-of-Plane Investigation of Resonant Tunneling Polaritons in Metal-Dielectric-Metal Cavities.

Polaritons can be generated by tuning the optical transitions of a light emitter to the resonances of a photonic cavity. We show that a dye-doped cavity generates resonant tunneling polaritons with Epsilon-Near-Zero (ENZ) effective permittivity. We studied the polariton spectral dispersion in dye-doped metal-dielectric-metal (MDM) cavities as a function of the in-plane (k||) and out-of-plane (k⊥) components of the incident wavevector. The dependence on k|| was investigated through ellipsometry, revealing the ENZ modes. The k⊥ dependence was measured by varying the cavity thickness under normal incidence using a Surface Force Apparatus (SFA). Both methods revealed a large Rabi splitting well exceeding 100 meV. The SFA-based investigation highlighted the collective nature of strong coupling by producing a splitting proportional to the square root of the involved photons. This study demonstrates the possibility of generating ENZ polaritons and introduces the SFA as a powerful tool for the characterization of strong light-matter interactions.

Anomalous Reflection From a Phase Gradient Metasurface With Arbitrary Incident Angle

A planar phase gradient metasurface (PGM) with phase gradients in two in-plane directions will introduce two additional wave vectors to the reflected wave vector. For small incident angles, close to the normal vector, the magnitude of the reflected wave vector is smaller than that of the incident wave vector and the direction of the anomalous reflected wave can be determined from the incident wave vector components and additional phase gradient components. The expanded generalized Snell’s law, which includes diffraction order modes, is combined with array theory to accurately predict the directions of the reflected waves from a planar PGM for incident angles where the magnitude of the reflected wave vector is larger than that of the incident wave vector. The predicted directions of the reflected waves from a planar PGM are compared with simulated RCS results obtained with CST Studio Suite and measured results obtained in a compact range.

Electron-Sheet Metasurfaces for Reconfigurable Beam Patterns

Here, a beam-steering structure based on the interaction of antenna radiation with an electron sheet with swiftly moving electrons with a constant velocity is proposed and studied theoretically. Such electron-sheet metasurface, while uniform and homogeneous in its composition, has a dynamic surface conductivity that exhibits nonlocal response that is dependent on the tangential component of the wave vector impinging on it, and may offer a nonsymmetric conductivity distribution with respect of this wave vector component. As a result, asymmetric radiation patterns may be generated from a single magnetic current line source in the presence of such a metastructure. This effect, introduced by the electron sheet with fast-moving electrons on the radiation properties, can be tailored by modifying the number density and the constant velocity of these electron sheets. We explore the effects of the electron-sheet metasurface on the far-zone radiated field in the presence and absence of a perfect electric conducting ground plane. Some of the electromagnetic features, such as the tilt of radiation pattern in the far zone and the field distribution in the near zone, are also discussed. We envision that this reconfigurable beam steering method may find potential applications in THz, microwave, and optical technologies.

Plasmon emission by interlayer excitons in twisted bilayers: Effect of large plasmonic wavevector components

While the emission of localized plasmons is often treated in the real-space picture, working in wavevector space makes it possible to resolve the contributions of various plasmonic Fourier components. By calculating the rate of plasmon emission by interlayer excitons in twisted ${\mathrm{MoSe}}_{2}/{\mathrm{WSe}}_{2}$ van der Waals heterostructures as a function of plasmon localization, twist angle, and temperature, we show that a much wider range of exciton states can radiate into subwavelength plasmon modes than into free space. Most of the emission in this case takes place via plasmonic Fourier components that exceed the maximum photon wavevector in free space. We demonstrate that this provides an avenue for continued Purcell scaling of the emission rate with mode size. Furthermore, the scaling is well in excess of the Purcell trend for sufficiently large twist angles and strong plasmonic localization.

Numerical analysis of the spatial structure of Alfvén waves in a finite pressure plasma in a dipole magnetosphere

We have carried out a numerical analysis of the spatial structure of Alfvén waves in a finite pressure inhomogeneous plasma in a dipole model of the magnetosphere. We have considered three magnetosphere models differing in maximum plasma pressure and pressure gradient. The problem of wave eigenfrequencies was addressed. We have established that the poloidal frequency can be either greater or less than the toroidal frequency, depending on plasma pressure and its gradient. The problem of radial wave vector component eigenvalues was considered. We have found points of Alfvén wave reflection in various magnetosphere models. The wave propagation region in the cold plasma model is shown to be significantly narrower than that in models with finite plasma pressure. We have investigated the structure of the main Alfvén wave harmonic when its polarization changes in three magnetosphere models. A numerical study into the effect of plasma pressure on the structure of behavior of all Alfvén wave electric and magnetic field components has been carried out. We have established that for certain parameters of the magnetosphere model the magnetic field can have three nodes, whereas in the cold plasma model there is only one. Moreover, the longitudinal magnetic field component changes sign twice along the magnetic field line.

Численный анализ пространственной структуры альфвеновских волн в плазме конечного давления в дипольной магнитосфере

We have carried out a numerical analysis of the spatial structure of Alfvén waves in a finite pressure inhomogeneous plasma in a dipole model of the magnetosphere. We have considered three magnetosphere models differing in maximum plasma pressure and pressure gradient. The problem of wave eigenfrequencies was addressed. We have established that the poloidal frequency can be either greater or less than the toroidal frequency, depending on plasma pressure and its gradient. The problem of radial wave vector component eigenvalues was considered. We have found points of Alfvén wave reflection in various magnetosphere models. The wave propagation region in the cold plasma model is shown to be significantly narrower than that in models with finite plasma pressure. We have investigated the structure of the main Alfvén wave harmonic when its polarization changes in three magnetosphere models. A numerical study into the effect of plasma pressure on the structure of behavior of all Alfvén wave electric and magnetic field components has been carried out. We have established that for certain parameters of the magnetosphere model the magnetic field can have three nodes, whereas in the cold plasma model there is only one. Moreover, the longitudinal magnetic field component changes sign twice along the magnetic field line.

The current state of the theory of Pc1 range ULF pulsations in magnetospheric plasma with heavy ions: A review

The review considers the current state of the theory of short-period ULF waves in plasma with admixture of heavy ions (ions whose mass significantly exceeds the mass of protons). The presence of heavy ions influences the spectrum and propagation characteristics of waves in Pc1 range. We examine elements of the theory of quasi-parallel and quasi-perpendicular short-period ULF waves. It is usually suggested that quasi-parallel ion-cyclotron waves have a left circular polarization. Quasi-perpendicular ion-ion hybrid waves have linear polarization and can be poloidal and toroidal. We discuss the theory of an equatorial resonator for Pc1 waves and determine its size from the density of heavy ions. In the radial direction, the waves can be locked in the vicinity of the plasmapause or in the region of a local minimum in the density of heavy ions. The equatorial resonator for arbitrary values of the wave vector components is considered. We note that ion-ion hybrid waves, in contrast to Alfvén waves, have a large parallel component of the magnetic field.

Современное соcтояние теории УНЧ-пульсаций диапазона Рс1 в плазме магнитосферы с тяжелыми ионами: обзор

The review considers the current state of the theory of short-period ULF waves in plasma with admixture of heavy ions (ions whose mass significantly exceeds the mass of protons). The presence of heavy ions influences the spectrum and propagation characteristics of waves in Pc1 range. We examine elements of the theory of quasi-parallel and quasi-perpendicular short-period ULF waves. It is usually suggested that quasi-parallel ion-cyclotron waves have a left circular polarization. Quasi-perpendicular ion-ion hybrid waves have linear polarization and can be poloidal and toroidal. We discuss the theory of an equatorial resonator for Pc1 waves and determine its size from the density of heavy ions. In the radial direction, the waves can be locked in the vicinity of the plasmapause or in the region of a local minimum in the density of heavy ions. The equatorial resonator for arbitrary values of the wave vector components is considered. We note that ion-ion hybrid waves, in contrast to Alfvén waves, have a large parallel component of the magnetic field.

Insight into band structures for out-of-plane propagation of a 2D dispersive photonic crystal: the dispersive photonic crystal iterative method

A study of the band structures of a two-dimensional dispersive photonic crystal for out-of-plane propagation along with the dispersive photonic crystal iterative method are presented. In these calculations, the proposed method uses the plane wave expansion method as the foundation. The photonic crystal is a square array of circular cross-sectional dispersive MgO Lorentz single-pole rods. The band structures were calculated starting at the high symmetry points Γ , X, and M as a function of the oblique component of the propagation wave vector. The method used is discussed in detail, and a simple equation is presented for straightforward analytical calculations of points of the frequency bands in the transparency window, where the dielectric constant equals that of vacuum.

Engineering the radiative dynamics of thermalized excitons with metal interfaces

As a platform for optoelectronic devices based on exciton dynamics, monolayer transition metal dichalcogenides (TMDCs) are often placed near metal interfaces or inside planar cavities. While the radiative properties of point dipoles at metal interfaces has been studied extensively, those of excitons, which are delocalized and exhibit a temperature-dependent momentum distribution, lack a thorough treatment. Here, we analyze the emission properties of excitons in TMDCs near planar metal interfaces and explore their dependence on exciton center-of-mass momentum, transition dipole orientation, and temperature. Defining a characteristic energy scale k B T c = (ℏk)2/2m (k being the radiative wavevector and m the exciton mass), we find that at temperatures T ≫ T c and low densities where the momentum distribution can be characterized by Maxwell–Boltzmann statistics, the modified emission rates (normalized to free space) behave similarly to point dipoles. This similarity in behavior arises due to the broad nature of wavevector components making up the exciton and point dipole emission. On the other hand, the narrow momentum distribution of excitons for T < T c can result in significantly different emission behavior as compared to point dipoles. These differences can be further amplified by considering excitons with a Bose Einstein distribution at high phase space densities, such as in a condensate phase. We find suppression or enhancement of emission relative to the point dipole case by several orders of magnitude. These insights can help optimize the performance of optoelectronic devices that incorporate 2D semiconductors near metal electrodes and can inform future studies of exciton radiative dynamics at low temperatures. Additionally, these studies show that nanoscale optical cavities are a viable pathway to generating long-lifetime exciton states in TMDCs.