Scattering of infrared light by dielectric core-shell particles

Abstract

We study the scattering of infrared light by small dielectric core-shell particles taking an Al2O3 sphere with a CaO core as an example. The extinction efficiency of such a particle shows two intense series of resonances attached, respectively, to in-phase and out-of-phase multipolar polarizationinduced surface charges build-up, respectively, at the core-shell and the shell-vacuum interface. Both series, the character of the former may be labelled bonding and the character of the latter antibonding, give rise to anomalous scattering. For a given particle radius and filling factor the Poynting vector field shows therefore around two wave numbers the complex topology of this type of light scattering. Inside the particle the topology depends on the character of the resonance. The dissipation of energy inside the particle also reflects the core-shell structure. It depends on the resonance and shows strong spatial variations.

Surface mode hybridization in the optical response of core-shell particles

“…The extinction spectra we calculated with the goal of employing them as a charge diagnostics in a plasma are based on the complex dielectric functions of the real materials 34,35 . In our work on topological aspects of light scattering by dielectric core-shell particles 33 we found however dissipation to blur higher order bonding and antibonding resonances. For the present purpose we employ therefore dissipationless model dielectric functions with parameters chosen such that bonding and antibonding resonances can be clearly identified up to the third multipole order.…”

“…The expansions ( 8) and ( 9) going back to Aden and Kerker 17 are the basis of most applications of the Mie theory to spherical core-shell particles. In our previous work we also used them 33,34 . Their physical content however is not obvious.…”

“…It should be noted that in the standard expansion the coefficients f n , g n , v n , and w n reduce in the respective limits also to the Mie coefficients of a medium-embedded homogeneous shell particle and a shell-embedded corecavity 33 . What we have shown by working with a 2 n , b 2 n , c 2 n , and d 2 n and rewriting them in a particular manner is that the two limiting cases are actually two building blocks whose resonances are always virtually present.…”

“…In this paper we show that this is indeed the case. For the particular case of a spherical core-shell particle the hybridization scenario can be straightforwardly derived from the Mie theory by recasting the Mie coefficients 3,4,17,33 in a form resembling the diagonal elements of a matrix resolvent describing two hybridized energy levels. The derivation, valid for all multipole orders and thus applicable to arbitrarily sized particles, starts with a splitting of the electromagnetic fields inside the shell into two parts 23,24 , corresponding to the penetrating fields of an homogeneous particle made out of shell material and the scattering fields of a cavity filled with core material and sitting inside an homogeneous domain of shell material.…”

Plasmonic properties and energy flow in rounded hexahedral and octahedral nanoparticles

“…Analytical methods also have been used for analyzing other geometrical shapes, such as core-shell spheres [15] and circular cylinders [3,16]. Interestingly, novel particle functionalities and designs could be devised [3,17,18] by exploiting the near field setup and the Poynting streamline distribution.…”