Invisible nanowires with interfering electric and toroidal dipoles

Liu, Wei; Zhang, Jianfa; Lei, Bing; Hu, Haoran; Miroshnichenko, Andrey E.

doi:10.1364/ol.40.002293

Cited by 110 publications

(94 citation statements)

References 32 publications

(57 reference statements)

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“…Similar resonances were recently detected in the scattering spectra of dielectric nanoparticles 49 (Fig. 3i) and were also predicted for core-shell wires 74 and hybrid nanoparticles 66 . Computational studies showed that inhomogeneous dielectric environment perturbs the non-radiating charge-current configuration leading to directional emission.…”

Section: Radiating Properties Of Toroidal Multipolessupporting

confidence: 87%

Electromagnetic toroidal excitations in matter and free space

et al. 2016

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The toroidal dipole is a localized electromagnetic excitation, distinct from the magnetic and electric dipoles. While the electric dipole can be understood as a pair of opposite charges and the magnetic dipole as a current loop, the toroidal dipole corresponds to currents flowing on the surface of a torus. Toroidal dipoles provide physically significant contributions to the basic characteristics of matter including absorption, dispersion, and optical activity. Toroidal excitations also exist in free-space as spatially and temporally localized electromagnetic pulses propagating at the speed of light and interacting with matter. We review recent experimental observations of resonant toroidal dipole excitations in metamaterials and the discovery of anapoles, non-radiating current configurations involving toroidal dipoles. While certain fundamental and practical aspects of toroidal electrodynamics remain open for the moment, we envision that exploitation of toroidal response can have important implications for the fields of photonics, sensing, energy and information. IntroductionThe interactions of electromagnetic radiation with matter underpin some of the most important technologies today -from telecommunications to information processing and data storage; from spectroscopy and imaging to light-assisted manufacturing. Our understanding and description of the electromagnetic properties of matter traditionally involves the concept of electric and magnetic dipoles, as well as their more complex combinations, known as multipoles. Introduced by Maxwell and Lorentz and later refined by Jackson and Landau, this framework, termed the multipole expansion, is central in physics and is being routinely applied in the study of optical, condensed matter, atomic, nuclear phenomena and beyond 1 . Within this framework, electromagnetic media can be represented by a set of point-like multipole sources [2][3][4][5] . The commonly used set of multipoles comprises the electric and magnetic families, which can be represented by oscillating charges and loop currents respectively. Dynamic toroidal multipoles constitute a third independent family of elementary electromagnetic sources, rather than an alternative multipole expansion or higher-order corrections to the conventional electric and magnetic multipoles (see tutorial inset I).Introduced in 1958 by Y. B. Zeldovich, toroidal moments have been considered in systems of toroidal topology (see Fig. 1) and studied in the context of nuclear 6 , atomic 7 , and molecular physics 8 , classical electrodynamics 9,10 , and solid state physics 3 . In the field of electromagnetism, in particular, a number of works have led to the development of a complete theoretical framework for toroidal electrodynamics [11][12][13][14][15] and the prediction of exotic effects, including dynamic non-radiating charge current configurations 10 and non-reciprocal interactions 9 . Following recent experimental observations of toroidal contributions in the response of materials across the electromagnetic spectrum, dyn...

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Section: Radiating Properties Of Toroidal Multipolessupporting

confidence: 87%

Electromagnetic toroidal excitations in matter and free space

et al. 2016

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“…2(a): though at point D the overall dipolar scattering is negligible [P(a 1 ), dashed black curve], TD response T is dominant over P and this means that they cannot interfere totally in a destructive way, thus catcalling the scattering of each other [11,13]; As a result, besides P and T, there must be higher order correcting terms for P(a 1 ) as shown in Eq. (9).…”

Section: Td Excitation Within Homogenous and Isotropic Dielectric Parmentioning

confidence: 99%

“…Stimulated by the recent experimental demonstration of toroidal dipoles (TDs) excited on the platform of metamaterials consisting of specially organized split ring resonators [1], studies into TDs and more generally toroidal multipoles (TMs) within photonic nano-systems have attached surging attention [2][3][4][5][6][7][8][9][10][11][12][13]. Compared to conventional electric and magnetic multipoles, TMs can be viewed as poloidal currents flowing on the surface of a torus along its meridians, or as a series of magnetic dipoles (enclosed circulating currents) aligned along enclosed paths [14,15].…”

Section: Introductionmentioning

confidence: 99%

“…But this unfortunately leads to more or less a dogma that TMs can only be observed in carefully engineered compound structures and consequently there have been very few searches for the existence of TMs in simple individual structures [8]. Only recently it is shown decisively that TMs can be excited within single scattering particles of fundamental (spherical or cylindrical) shapes, which also have been proven to play indispensable roles for some exotic scattering properties [10,11,13]. The incorporation of TMs extends significantly our understanding of the fundamental problem of light scattering by spherical and cylindrical particles.…”

Section: Introductionmentioning

confidence: 99%

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Efficient excitation and tuning of toroidal dipoles within individual homogenous nanoparticles

et al. 2015

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Abstract:We revisit the fundamental topic of light scattering by single homogenous nanoparticles from the new perspective of excitation and manipulation of toroidal dipoles. It is revealed that besides within all-dielectric particles, toroidal dipoles can also be efficiently excited within homogenous metallic nanoparticles. Moreover, we show that those toroidal dipoles excited can be spectrally tuned through adjusting the radial anisotropy parameters of the materials, which paves the way for further more flexible manipulations of the toroidal responses within photonic systems. The study into toroidal multipole excitation and tuning within nanoparticles deepens our understanding of the seminal problem of light scattering, and may incubate many scattering related fundamental researches and applications.

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“…Superposition of dynamic electric and toroidal dipoles leads to anapoles which, through destructive interference, exhibit vanishing radiated fields outside the source [20,22]. Anapoles have been observed in microwave metamaterials [16] and dielectric nanoparticles [18], and their excitation has also been predicted in core-shell nanoparticles [23] and nanowires [24]. Moreover, anapoles have been employed to enhance nonlinear effects [25] and realize high-Q microwave metamaterials [26].…”

mentioning

confidence: 99%

Exciting dynamic anapoles with electromagnetic doughnut pulses

Raybould

Fedotov

Papasimakis

et al. 2017

Applied Physics Letters

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As was predicted in 1995 by Afanasiev and Stepanofsky, a superposition of electric and toroidal dipoles can lead to a non-trivial non-radiating charge current-configuration, the dynamic anapole. The anapoles were recently observed first in microwave metamaterials and then in dielectric nanodisks. However, spectroscopic studies of toroidal dipole and anapole excitations are challenging owing to their diminishing coupling to transverse electromagnetic waves. Here, we show that anapoles can be excited by electromagnetic Flying Doughnut (FD) pulses. First described by Helwarth and Nouchi in 1996, FD pulses are space-time inseparable exact solutions to Maxwells equations that have toroidal topology and propagate in free-space at the speed of light. We argue that FD pulses can be used as a diagnostic and spectroscopic tool for the anapole excitations in matter.Flying Doughnut (FD) pulses were introduced by Hellwarth and Nouchi in 1996 [1] as exact solutions to Maxwells equations in free-space [2][3][4][5][6][7][8][9]. They are necessarily few-cycle, wideband electromagnetic perturbations with toroidal field topology that can exist in transverse electric (TE) and transverse magnetic (TM) configurations [1,10]. FD pulses can be seen as propagating counterparts of the localized toroidal dipole excitations in matter [11]. The toroidal dipole is distinct from the conventional electric and magnetic dipoles [12,13] and have attracted significant interest in recent years as important contributors to the electromagnetic properties of media with non-local response or elements of toroidal symmetry [11,[14][15][16][17][18][19][20][21]. Superposition of dynamic electric and toroidal dipoles leads to anapoles which, through destructive interference, exhibit vanishing radiated fields outside the source [20,22]. Anapoles have been observed in microwave metamaterials [16] and dielectric nanoparticles [18], and their excitation has also been predicted in core-shell nanoparticles [23] and nanowires [24]. Moreover, anapoles have been employed to enhance nonlinear effects [25] and realize high-Q microwave metamaterials [26]. However, anapole modes are weakly coupled to freespace radiation, which renders experimental observations particularly challenging. In this paper, we demonstrate numerically the excitation of anapoles in a spherical dielectric particle driven by an FD pulse.We consider a dispersionless spherical dielectric particle interacting with a TM FD pulse, as depicted in Fig. 1. The FD pulse is brought to focus on the dielectric sphere located at the origin of the coordinate system. The interactions between FD pulses and dielectric spherical particles are investigated by a finite element solver of Maxwell's equations in three dimensions. The simulations are conducted in the transient domain. We define the incident FD pulse as per the field prescriptions in ref. (1)where σ = z + ct and τ = z − ct, and f 0 is an arbitrary normalisation constant. The parameters q 1 and q 2 have dimensions of length and represent respectively the ...

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Invisible nanowires with interfering electric and toroidal dipoles

Cited by 110 publications

References 32 publications

Electromagnetic toroidal excitations in matter and free space

Electromagnetic toroidal excitations in matter and free space

Efficient excitation and tuning of toroidal dipoles within individual homogenous nanoparticles

Exciting dynamic anapoles with electromagnetic doughnut pulses

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