Magnetic and electric coherence in forward- and back-scattered electromagnetic waves by a single dielectric subwavelength sphere

Abstract

Magnetodielectric small spheres present unusual electromagnetic scattering features, theoretically predicted a few decades ago. However, achieving such behaviour has remained elusive, due to the non-magnetic character of natural optical materials or the difficulty in obtaining low-loss highly permeable magnetic materials in the gigahertz regime. Here we present unambiguous experimental evidence that a single low-loss dielectric subwavelength sphere of moderate refractive index (n ¼ 4 like some semiconductors at near-infrared) radiates fields identical to those from equal amplitude crossed electric and magnetic dipoles, and indistinguishable from those of ideal magnetodielectric spheres. The measured scattering radiation patterns and degree of linear polarization (3-9 GHz/33-100 mm range) show that, by appropriately tuning the a/l ratio, zero-backward ('Huygens' source) or almost zeroforward ('Huygens' reflector) radiated power can be obtained. These Kerker scattering conditions only depend on a/l. Our results open new technological challenges from nanoand micro-photonics to science and engineering of antennas, metamaterials and electromagnetic devices.

Directional visible light scattering by silicon nanoparticles

“…Very recently first experimental demonstration of Kerker'stype scattering by high-refractive index dielectric particles has been published 35 . These results were obtained in GHz frequency range with millimetre-size particles.…”

Monodisperse silicon nanocavities and photonic crystals with magnetic response in the optical region

“…Theoretical results on full dielectric optical antennas 28,29 , magnetic type optical trapping 25 and metamaterials-related devices 22,23 have been published. Very recently, it has been reported about the directional scattering properties of high refractive index nanoparticles produced by simultaneous excitation and mutual interference of magnetic and electric dipole resonances inside a single high refractive index particle [33][34][35] , which is a strong evidence of the magnetic response of silicon colloids at optical frequencies. Owing to the welldefined optical resonant modes, high refractive index colloids, whose size is much smaller than the wavelength of light, behave as photonic nanocavities.…”

Optical theorem for the conservation of electromagnetic helicity: Significance for molecular energy transfer and enantiomeric discrimination by circular dichroism

“…In the emerging field of silicon photonics with magnetodielectric structures, the behavior of g and g H drastically changes since then the resonant α I m associated to the excitation of the magnetic dipole [36,[41][42][43][44][45], would dominate α I e and α R em ; thus g may diminish while g H would be enhanced. Further advances in the study of magnetodielectric chiral objects should manifest such effects.…”

“…Increasingly investigated structures with electric and magnetic dipoles [36,[42][43][44], and their mutual interaction [34,41,44,45], make (34) of appealing and intriguing consequences in such future studies. The details on these quantities will be the subject of a future study.…”

“…(31), states that the particle is dual [6,7], i.e. ǫ −1 α e = µα m and thus fulfills the well-known first Kerker condition (K1) [40,41] according to which it produces zero angular distribution of scattered intensity in the backscattering direction. However, as seen next, this also occurs for chiral particles.…”