Multipoles Of Different Orders Research Articles

Enhanced Spin Hall Shift by Multipoles of Different Orders in Spherical Particles

The spin–orbit interaction of light is universal in the process of light scattering, and an important aspect is the spin Hall effect. The spin Hall effect of light also exists in a three-dimensional (3D) system. When circularly polarized light is incident on a spherical particle, the transverse displacement of the particle relative to the scattering plane can be observed due to the spiraling of the Poynting vector in the far field. In general, the spin Hall shift of light is negligible and difficult to detect in experiments. In this paper, we use a high-refractive-index (HRI) core-shell structure to excite high-order multipoles and explore the interaction between different order multipoles to enhance the spin Hall shift in the microwave band. We show that there exist some angles that increase the spin Hall shift when two particular multipoles are equal and dominated. Our work provides a new perspective for understanding the interaction between light and particles and enhances the spin Hall shift of the sphere in the microwave band.

Ideal Kerker scattering by homogeneous spheres: the role of gain or loss.

We investigate how the optical gain or loss (characterized by isotropic complex refractive indexes) influence the ideal Kerker scattering of exactly zero backward scattering. It was previously shown that, for non-magnetic homogeneous spheres with incident plane waves, either gain or loss prohibit ideal Kerker scattering, provided that only electric and magnetic multipoles of a specific order are present and contributions from other multipoles can all be made precisely zero. Here we reveal that, when two multipoles of a fixed order are perfectly matched in terms of both phase and magnitude, multipoles of at least the next two orders cannot possibly be tuned to be all precisely zero or even perfectly matched, and consequently cannot directly produce ideal Kerker scattering. Moreover, we further demonstrate that, when multipoles of different orders are simultaneously taken into consideration, loss or gain can serve as helpful rather than harmful contributing factors, for the elimination of backward scattering.

Toroidal‐Assisted Generalized Huygens’ Sources for Highly Transmissive Plasmonic Metasurfaces

AbstractMetasurface operating in the transmission scheme has shown a promising scenario for flat optics applications. Nevertheless, the inherently low working efficiency of transmissive plasmonic metasurfaces at optical frequencies severely hinders them from future technology development. This work reports on a hybrid plasmonic meta‐atom (HPMA) with a simple fabrication and cost‐effective single‐lithographic process featuring a toroidal‐assisted generalized Huygens’ source with a state‐of‐the‐art circular polarization conversion efficiency beyond 50%. The HPMA representsa new upper limit for transmission efficiency in the near‐infrared. The high transmission is realized via balanced multipoles of different orders including toroidal dipole that satisfies the generalized Kerker condition. The introduction of toroidal dipole provides an additional degree of freedom to tailor the wave interference and radiation symmetry rather than the use of a conventional electric and magnetic multipolar coupling. In addition, two high‐performance metasurfaces by combining the HPMAs with the geometric phase method are highlighted. The highly‐transmissive beam deflection metasurface and plasmonic metalens respectively yield anomalous refraction with 38.2% optical efficiency and 46.56% focusing efficiency, both experimentally showing a record transmission level. The findings may open new ways to design highly‐efficient plasmonic metasurfaces and to take one step forward to facilitate nearly optimal and practical nanophotonic devices.

Light Absorption and Scattering Spectra of Gold Nanospheres Coated with TDBC J-Aggregates

Light absorption and scattering spectra of gold nanospheres coated with J-aggregates of TDBC dye are calculated. The effect of multipoles of different orders on the intensity distribution in absorption spectra due to the plasmon—exciton coupling of the nucleus and particle shell was established. The contributions of light absorption and scattering to the extinction cross section are determined.

Colloidal interactions and unusual crystallization versus de-mixing of elastic multipoles formed by gold mesoflowers

Colloidal interactions in nematic liquid crystals can be described as interactions between elastic multipoles that depend on particle shape, topology, chirality, boundary conditions and induced topological defects. Here, we describe a nematic colloidal system consisting of mesostructures of gold capable of inducing elastic multipoles of different order. Elastic monopoles are formed by relatively large asymmetric mesoflower particles, for which gravity and elastic torque balancing yields monopole-type interactions. High-order multipoles are instead formed by smaller mesoflowers with a myriad of shapes corresponding to multipoles of different orders, consistent with our computer simulations based on free energy minimization. We reveal unexpected many-body interactions in this colloidal system, ranging from de-mixing of elastic monopoles to a zoo of unusual colloidal crystals formed by high-order multipoles like hexadecapoles. Our findings show that gold mesoflowers may serve as a designer toolkit for engineering colloidal interaction and self-assembly, potentially exceeding that in atomic and molecular systems.

Attenuation Regularities of Vector-Scalar Fields of Multipole Sources in Interference Maxima Regions

Limiting dependences determining the attenuation regularities (related to an increase in distance) of sound pressure and orthogonal components of vibration velocity vector in the regions of interference maxima of signals formed in a Pekeris waveguide by multipoles of different orders, have been obtained and numerically analyzed.

Generalized Kerker effects in nanophotonics and meta-optics [Invited

The original Kerker effect was introduced for a hypothetical magnetic sphere, and initially it did not attract much attention due to a lack of magnetic materials required. Rejuvenated by the recent explosive development of the field of metamaterials and especially its core concept of optically-induced artificial magnetism, the Kerker effect has gained an unprecedented impetus and rapidly pervaded different branches of nanophotonics. At the same time, the concept behind the effect itself has also been significantly expanded and generalized. Here we review the physics and various manifestations of the generalized Kerker effects, including the progress in the emerging field of meta-optics that focuses on interferences of electromagnetic multipoles of different orders and origins. We discuss not only the scattering by individual particles and particle clusters, but also the manipulation of reflection, transmission, diffraction, and absorption for metalattices and metasurfaces, revealing how various optical phenomena observed recently are all ubiquitously related to the Kerker's concept.

Diffraction of the quasi-static antenna field by a sphere in near-field microwave probing

The theory of near-field (NF) location of a sphere of an arbitrary diameter dsph is developed. This theory is used to calculate the impedance of an antenna of small wave diameter D in the case when a spherical contrast object is located at distance h in the antenna near-field zone. It is shown that excitation of multipole modes in the sphere perturbs the impedance, which determines the response of a locator to the studied object. The contributions from radiations of electric and magnetic multipoles of different orders to the impedance is analyzed as a function of parameters dsph/D and h/D. It is found that, for fixed parameters of the antenna-sphere system, number n* of multipoles that should be taken into account is finite and functions n*(dsph/D) and n*(h/D) are determined. The limits of applicability of the electric-dipole (Rayleigh) approximation in calculation of near-field diffraction are determined. The conditions of resonant excitation of multipole modes, which is accompanied by a sharp increase in the real part of the antenna impedance, are found. The developed theory is used to analyze the prospects for application of the NF locator for detection of a cancerous tumor inside the human body. It is shown that, in the case of optimal selection of the device parameters, excitation of higher-order multipoles increases the detection range, which is ∼1.3 cm for a tumor size of 1–1.5 cm.

The role of the solar magnetic field systems in modulating the solar irradiance

Variations of indices that characterize various systems of the large-scale solar magnetic field (LSSMF) - magnetic field multipoles of different order, LSSMF energy index, index of the effective solar multipole, etc.- are compared with variations of the solar irradiance in different frequency ranges during 1978–1996. The role of the local and global magnetic fields in modulating the solar irradiance is investigated in various time intervals, in particular, in different phases of the 11-year solar cycle.

Emission by multipoles: an exact result in terms of reducible multipoles

On the basis of an expression for the (time-averaged) radiated power comprising the radiation sources at the retarded time, an exact expression relevant to the emission by reducible multipoles is obtained, which, along with the emission from independent multipoles, accounts for the emission from the interaction between multipoles of different order. Whereas the former contribution is known in literature, at least for the lower-order multipoles, the latter contribution so far appears to have been overlooked. The result thus obtained is discussed in reference to the treatment of multipole emission in terms of irreducible multipoles, generalized to non-monochromatic sources.

Pattern analysis of paraboloids fed by rectangular waveguides employing multipole expansion techniques

A multipole expansion technqiue is developed for calculating the co-polar and cross-polar radiation patterns of a prime-focus paraboloid fed by a dominant-mode rectangular waveguide feed. Initially, the feed radiation pattern is expressed in terms of electric and magnetic multipoles of different orders which are subsequently used to obtain the secondary radiation patterns (co-polar and cross-polar) in explicit closed form in the form of a rapid by a converging algebraic series. The validity of the analysis is effectively demonstrated by calculating the co-polar and cross-polar patterns of a typical paraboloid and comparing and results with calculations based on the direct numerical integration of the physical optics currents induced on the reflector surface.

Multipole expansion of the retarded interatomic dispersion energy

Abstract The multipole expansion of the retarded dispersion energy of two atoms in non-degenerate ground states is derived. The result shows that multipoles of different order may give rise to dispersion energies varying in the same way for large interatomic separations.