### Browsing by Author "Tzarouchis, Dimitrios"

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Item Light scattering by a dielectric sphere: Perspectives on the Mie resonances(2018-01-26) Tzarouchis, Dimitrios; Sihvola, Ari; Department of Electronics and Nanoengineering; Ari Sihvola GroupLight scattering by a small spherical particle, a central topic for electromagnetic scattering theory, is here considered. In this short review, some of the basic features of its resonant scattering behavior are covered. First, a general physical picture is described by a full electrodynamic perspective, the Lorenz-Mie theory. The resonant spectrum of a dielectric sphere reveals the existence of two distinctive types of polarization enhancement: the plasmonic and the dielectric resonances. The corresponding electrostatic (Rayleigh) picture is analyzed and the polarizability of a homogeneous spherical inclusion is extracted. This description facilitates the identification of the first type of resonance, i.e., the localized surface plasmon (plasmonic) resonance, as a function of the permittivity. Moreover, the electrostatic picture is linked with the plasmon hybridization model through the case of a step-inhomogeneous structure, i.e., a core-shell sphere. The connections between the electrostatic and electrodynamic models are reviewed in the small size limit and details on size-induced aspects, such as the dynamic depolarization and the radiation reaction on a small sphere are exposed through the newly introduced Mie-Padé approximative perspective. The applicability of this approximation is further expanded including the second type of resonances, i.e., the dielectric resonances. For this type of resonances, the Mie-Padé approximation reveals the main character of the two different cases of resonances of either magnetic or electric origin. A unified picture is therefore described encompassing both plasmonic and dielectric resonances, and the resonant conditions of all three different types are extracted as functions of the permittivity and the size of the sphere. Lastly, the directional scattering behavior of the first two dielectric resonances is exposed in a simple manner, namely the Kerker conditions for maximum forward and backscattering between the first magnetic and electric dipole contributions of a dielectric sphere. The presented results address several prominent functional features, aiming at readers with either theoretical or applied interest for the scattering aspects of a resonant sphere.Item Polarizability and Light Scattering by Subwavelength Graded-Index Plasmonic Spheres(2018) Tzarouchis, Dimitrios; Sihvola, Ari; Department of Electronics and NanoengineeringLight scattering by a subwavelength sphere exhibiting radially inhomogeneous permittivity is here presented. The theoretical foundations describing the scattering response are given in a simple manner and the concept of polarizability is generalized incorporating the inhomogeneity effects. Two illustrative examples are briefly discussed, i.e., a power-law and a Drude-like inhomogeneous profile, exposing the physical mechanisms of their scattering response. The presented results can open the path towards the implementation of graded-index subwavelength particles in modern nanoantenna applications.Item Spurious-Free Surface Integral Equation Characteristic Mode Formulation for Dielectric Bodies(2018) Ylä-Oijala, Pasi; Tzarouchis, Dimitrios; Wallén, Henrik; Sihvola, Ari; Keijo Nikoskinen Group; Department of Electronics and NanoengineeringA new surface integral equation based formulation for computing characteristic modes of lossless and lossy dielectric and magneto-dielectric bodies is presented. For lossy objects, the imaginary part of an eigenvalue gives the ratio of the dissipated and radiated power, while the real part is connected to the ratio of the reactive and radiated power.Item Subwavelength hexahedral plasmonic scatterers(MDPI AG, 2019-02-25) Tzarouchis, Dimitrios; Ylä-Oijala, Pasi; Sihvola, Ari; Department of Electronics and NanoengineeringIn this work, we investigate the resonant characteristics of hexahedral (cubical) inclusions at the plasmonic domain. After an introduction to the notion of superquadric surfaces, i.e., surfaces that model various versions of a rounded cube, we present the main resonant spectrum and the surface distributions for two particular cases of a smooth and a sharp cube in the plasmonic domain. We present a historical comparative overview of the main contributions available since the 1970s. A new categorization scheme of the resonances of a cube is introduced, based on symmetry considerations. The obtained results are compared against several recent works, exposing that the higher-order modes are extremely susceptible to both the choice of sharpness of the cube and the modeling mesh. This work can be readily used as a reference for both historical and contemporary studies of the plasmonic aspects of a cube.