Pascale, Mariano
(2021)
MaterialIndependent Modes for the Electromagnetic Scattering From Homogeneous Objects: from Quasistatic to FullWave Formulations.
[Tesi di dottorato]
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Item Type: 
Tesi di dottorato

Resource language: 
English 
Title: 
MaterialIndependent Modes for the Electromagnetic Scattering From Homogeneous Objects: from Quasistatic to FullWave Formulations 
Creators: 
Creators  Email 

Pascale, Mariano  mariano.pascale@unina.it 

Date: 
6 July 2021 
Number of Pages: 
190 
Institution: 
Università degli Studi di Napoli Federico II 
Department: 
Ingegneria Elettrica e delle Tecnologie dell'Informazione 
Dottorato: 
Information technology and electrical engineering 
Ciclo di dottorato: 
33 
Coordinatore del Corso di dottorato: 
nome  email 

Riccio, Daniele  daniele.riccio@unina.it 

Tutor: 
nome  email 

Forestiere, Carlo  UNSPECIFIED 

Date: 
6 July 2021 
Number of Pages: 
190 
Keywords: 
NanophotonicsNanoplasmonicsElectromagnetic scattering theorySpectral theory 
Settori scientificodisciplinari del MIUR: 
Area 09  Ingegneria industriale e dell'informazione > INGIND/31  Elettrotecnica 
Date Deposited: 
27 Jul 2021 15:33 
Last Modified: 
07 Jun 2023 10:29 
URI: 
http://www.fedoa.unina.it/id/eprint/13991 
Collection description
The light manipulation at the nanoscale is the leitmotif of the research field of nanophotonics. Over the last decades, the classical limits imposed by diffraction have been largely surpassed by virtue of technological and theoretical breakthroughs in the field of lightmatter interaction. Properly engineered metallic and dielectric nanostructures provide an unprecedented level of control over the electromagnetic radiation in subwavelength spatial regions. This is enabled by their resonant behavior at the optical frequencies. Thus, the development in this research field necessarily depends on an effective electromagnetic modeling of these resonances.
Hand in hand with the technological progress, there have been growing efforts in providing a complete and accurate framework for the description of resonances in metallic and dielectric nanostructures. The most powerful tools have certainly been represented by the spectral theories, in which the object electromagnetic behavior is characterized by its resonant modes. These modes are calculated as solutions of an auxiliary eigenvalue problem, i.e., the sourcefree Maxwell's equations.
Several spectral theories have been developed, and in each of them the nanostructure geometric parameters, material, and resonant frequencies are intertwined in a different way, according to the choice of spectral parameter. For instance, the quasinormal modes, widespread in the nanophotonics community, adopt, as the spectral parameter, the operating frequency, and hence the modes depend on both the nanostructure material and its shape.
In the recent years, a spectral method that uses the object relative permittivity as spectral parameter, has proved very useful in the modeling of the electromagnetic scattering from homogeneous isotropic nanostructures. This method relies on modes, called materialindependent modes, that depend on the object geometry and the operating frequency, but not on the nanostructure dielectric permittivity.
The goal of this thesis is to develop the description of electromagnetic scattering by homogeneous objects in terms of materialindependent modes.
In Chapter 1, we briefly review recent highlights in the modeling and applications of resonant metallic and dielectric nanostructures, and contextualize the spectral theory of the materialindependent modes.
In Chapter 2, we develop the formalism to describe the resonances in objects smaller than the incident wavelength. Specifically, we show that the resonances in metal and dielectric nanostructures of any shape are electro and magnetoquasistatic in nature, respectively, and can be described through eigenfunctions (quasistatic modes) of compact and selfadjoint integral operators. Through means of a perturbative approach, we then provide an extension to the quasistatic analysis, and we link the radiation corrections to the frequency shift and radiation quality (Q) factor of the quasistatic modes, through closedform expressions. In the derived expressions, the dependencies on the material and the size of the object are factorized.
In Chapter 3, we exploit the quasistatic mode framework introduced in the previous chapter for the calculation of the optimal current distribution supported by an object of dimension smaller than the wavelength, yelding the minimum Q factor. The provided representation leads to analytical and closed form expressions of the electric and magnetic polarizability tensors of arbitrary shaped objects, whose eigenvalues are known to be linked to the minimum Q factor. Many examples are worked out, in threedimensional, twodimensional (surfaces), and translational invariant objects.
In Chapter 4, we introduce the fullwave materialindependent modes for the description of the scattering from an arbitrary sized 3D object. As a case of study, we investigate the modes and resonances of the prototypical structure of a sphere. We show how the analysis of the object modes and eigenvalues provides a systematic classification of resonances and interference effects. In particular, in this framework, we are able to justify the differences in the power spectrum scattered by dielectric and metal nanoparticles.
In Chapter 5, we investigate the resonances and resonance modes in the electromagnetic scattering from metallic and dielectric sphere dimers in the fullwave regime, by using the materialindependent modes. Along the lines of the wellknown plasmon hybridization model, we see the dimer modes as the result of the hybridization of the modes of the two constituent spheres, whose importance is quantified by hybridization weights. In this way, as we vary the spheres arrangement, although the dimer modes change, they are still represented in terms of the same set of singlesphere modes, but with different hybridization weights. This study represents the first fullMaxwell theory of hybridization in dielectric dimers, and it also constitutes an extension of the plasmonmode hybridization theory.
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