scholarly journals Spin photonics: from transverse spin to photonic skyrmions

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Peng Shi ◽  
Luping Du ◽  
Xiaocong Yuan
Keyword(s):  
Electromagnetic Waves ◽  
Guided Waves ◽  
Spin Dynamics ◽  
Near Field ◽  
Longitudinal Optical ◽  
Transverse Spin ◽  
Strongly Coupled ◽  
Spin Structures ◽  
Structures And Properties ◽  
The Mean

Abstract Spin angular momentum associated with circular polarization is a fundamental and important aspect of photons both in classical and quantum optics. The interaction of this optical spin with matter and structures results in many intriguing optical effects and state-of-the-art applications covered under the emerging subject of spin optics. Distinct from longitudinal optical spin along the mean wavevector, transverse spin, the corresponding vector of which is perpendicular to the mean wavevector, prevails and plays a significant role in confined electromagnetic waves such as focused beams, guided waves, and evanescent waves. In the optical near-field, these transverse spins are generated owing to the spatial variation of the kinetic momentum of confined electromagnetic waves, where the spin and orbital angular momenta are strongly coupled, leading to many interesting topological spin structures and properties. Several reviews on optical transverse spins have been published in recent years in which their concepts and the various configurations producing them were introduced systematically. Here, we introduce in this review the underlying physics and dynamics of transverse spin and the resultant topological structures and properties such as the photonic skyrmions and merons. We term this sub-area ‘spin photonics’, its scope being to cover the design and research of spin structures in strongly confined electromagnetic fields with unique properties and applications. The concepts and framework reviewed have importance in optics, topological photonics, metrology, and quantum technologies and may be used to extend spin-dynamics concepts to fluidic, acoustic, and gravitational waves.

scholarly journals Transverse spin dynamics in structured electromagnetic guided waves

2021 ◽  
Vol 118 (6) ◽  
pp. e2018816118
Author(s):  
Peng Shi ◽  
Luping Du ◽  
Congcong Li ◽  
Anatoly V. Zayats ◽  
Xiaocong Yuan
Keyword(s):  
Electromagnetic Waves ◽  
Vector Fields ◽  
Spin Dynamics ◽  
Complex Structure ◽  
Practical Importance ◽  
Surface States ◽  
Transverse Spin ◽  
Topological Properties ◽  
Guided Modes ◽  
Spin Momentum

Spin–momentum locking, a manifestation of topological properties that governs the behavior of surface states, was studied intensively in condensed-matter physics and optics, resulting in the discovery of topological insulators and related effects and their photonic counterparts. In addition to spin, optical waves may have complex structure of vector fields associated with orbital angular momentum or nonuniform intensity variations. Here, we derive a set of spin–momentum equations which describes the relationship between the spin and orbital properties of arbitrary complex electromagnetic guided modes. The predicted photonic spin dynamics is experimentally verified with four kinds of nondiffracting surface structured waves. In contrast to the one-dimensional uniform spin of a guided plane wave, a two-dimensional chiral spin swirl is observed for structured guided modes. The proposed framework opens up opportunities for designing the spin structure and topological properties of electromagnetic waves with practical importance in spin optics, topological photonics, metrology and quantum technologies and may be used to extend the spin-dynamics concepts to fluid, acoustic, and gravitational waves.

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

scholarly journals Whistler intensities above thunderstorms

2010 ◽  
Vol 28 (1) ◽  
pp. 37-46 ◽  
Author(s):  
J. Fiser ◽  
J. Chum ◽  
G. Diendorfer ◽  
M. Parrot ◽  
O. Santolik
Keyword(s):  
Background Noise ◽  
Electromagnetic Waves ◽  
Horizontal Distance ◽  
Average Amplitude ◽  
Oblique Propagation ◽  
Lightning Current ◽  
Processing Data ◽  
Demeter Satellite ◽  
Late Evening ◽  
The Mean

Abstract. We report a study of penetration of the VLF electromagnetic waves induced by lightning to the ionosphere. We compare the fractional hop whistlers recorded by the ICE experiment onboard the DEMETER satellite with lightning detected by the EUCLID detection network. To identify the fractional hop whistlers, we have developed software for automatic detection of the fractional-hop whistlers in the VLF spectrograms. This software provides the detection times of the fractional hop whistlers and the average amplitudes of these whistlers. Matching the lightning and whistler data, we find the pairs of causative lightning and corresponding whistler. Processing data from ~200 DEMETER passes over the European region we obtain a map of mean amplitudes of whistler electric field as a function of latitudinal and longitudinal difference between the location of the causative lightning and satellite magnetic footprint. We find that mean whistler amplitude monotonically decreases with horizontal distance up to ~1000 km from the lightning source. At larger distances, the mean whistler amplitude usually merges into the background noise and the whistlers become undetectable. The maximum of whistler intensities is shifted from the satellite magnetic footprint ~1° owing to the oblique propagation. The average amplitude of whistlers increases with the lightning current. At nighttime (late evening), the average amplitude of whistlers is about three times higher than during the daytime (late morning) for the same lightning current.

scholarly journals Transverse Spin Dynamics in the Anisotropic Heisenberg Model Realized with Ultracold Atoms

2021 ◽  
Vol 11 (4) ◽  
Author(s):  
Paul Niklas Jepsen ◽  
Wen Wei Ho ◽  
Jesse Amato-Grill ◽  
Ivana Dimitrova ◽  
Eugene Demler ◽  
...  
Keyword(s):  
Heisenberg Model ◽  
Ultracold Atoms ◽  
Spin Dynamics ◽  
Transverse Spin ◽  
Anisotropic Heisenberg Model

WISDOM Antenna Pattern in the presence of Rover and Soil

2021 ◽  
Author(s):  
Wolf-Stefan Benedix ◽  
Dirk Plettemeier ◽  
Christoph Statz ◽  
Yun Lu ◽  
Ronny Hahnel ◽  
...  
Keyword(s):  
Pattern Matching ◽  
Ground Penetrating Radar ◽  
Electromagnetic Waves ◽  
Complete System ◽  
Near Field ◽  
System Model ◽  
Soil Types ◽  
Broadband Antenna ◽  
Shallow Subsurface ◽  
Ground Penetrating

<p>The WISDOM ground-penetrating radar aboard the 2022 ESA-Roscosmos Rosalind-Franklin ExoMars Rover will probe the shallow subsurface of Oxia Planum using electromagnetic waves. A dual-polarized broadband antenna assembly transmits the WISDOM signal into the Martian subsurface and receives the return signal. This antenna assembly has been extensively tested and characterized w.r.t. the most significant antenna parameters (gain, pattern, matching). However, during the design phase, these parameters were simulated or measured without the environment, i.e., in the absence of other objects like brackets, rover vehicle, or soil. Some measurements of the rover's influence on the WISDOM data were performed during the instrument's integration.</p><p>It was shown that the rover structure and close surroundings in the near-field region of the WISDOM antenna assembly have a significant impact on the WISDOM signal and sounding performance. Hence, it is essential to include the simulations' environment, especially with varying surface and underground.</p><p>With this contribution, we outline the influences of rover and ground on the antenna's pattern and particularly on the footprint. We employ a 3D field solver with a complete system model above different soil types, i.e., subsurface materials with various combinations of permittivity and conductivity.</p>

scholarly journals Efficient and Compact Near-Field Coupled Hybrid Antenna Using a Single Radiating Subwavelength Split-Ring Resonator

Electronics ◽  
2019 ◽  
Vol 8 (5) ◽  
pp. 527
Author(s):  
Zinching Dang ◽  
Marco Rahm
Keyword(s):  
Resonance Frequency ◽  
Electromagnetic Waves ◽  
Ring Resonator ◽  
Near Field ◽  
Low Frequency ◽  
Split Ring Resonator ◽  
Dipole Antenna ◽  
Angular Width ◽  
Split Ring ◽  
Broadband Internet

Modern applications in the realms of wireless communication and mobile broadband Internet increase the demand for compact antennas with well defined directivity. Here, we present an approach for the design and implementation of hybrid antennas consisting of a classic feeding antenna that is near-field-coupled to a subwavelength resonator. In such a combined structure, the composite antenna always radiates at the resonance frequency of the subwavelength oscillator as well as at the resonance frequency of the feeding antenna. While the classic antenna serves as impedance-matched feeding element, the subwavelength resonator induces an additional resonance to the composite antenna. In general, these near-field coupled structures are known for decades and are lately published as near-field resonant parasitic antennas. We describe an antenna design consisting of a high-frequency electric dipole antenna at f d = 25 GHz that couples to a low-frequency subwavelength split-ring resonator, which emits electromagnetic waves at f SRR = 10.41 GHz. The radiating part of the antenna has a size of approximately 3.2 mm × 8 mm × 1 mm and thus is electrically small at this frequency with a product k · a = 0.5 . The input return loss of the antenna was moderate at − 18 dB and it radiated at a spectral bandwidth of 120 MHz. The measured main lobe of the antenna was observed at 60 ∘ with a − 3 dB angular width of 65 ∘ in the E-plane and at 130 ∘ with a − 3 dB angular width of 145 ∘ in the H-plane.

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