28 Juin – Thesis defense - Maxime Bertrand

14 h Amphi - Institut d’Optique d’Aquitaine (Talence)

Electromagnetic modeling of nanoparticle-based complex media and metasurfaces: the global polarizability matrix method.

A great variety of electromagnetic nanoparticles, possibly mixing dielectric and metallic materials and having a complex shape, can nowadays be synthesized on large quantities by colloidal means and then self-assembled in stratified media. These complex photonic and plasmonic nanostructures offer a wide panel of optical functionalities, such as control of light emission, absorption or diffuse scattering, thanks to the optical resonances of the individual particles, their interaction with the interfaces and their mutual interaction via free space and guided modes.

Predicting quantitatively the optical response of such complex nanostructures is however a real challence because it requires being able to model coherent phenomena at both levels of a particle (nano-scale) and of an ensemble of interacting particles (meso-scale). The present manuscript introduces a new numerical method, named Global Polarizability Matrix (GPM) method, developed during this thesis to tackle this challenge. The method consists of finding a small set of fictitious polarizable elements - or "numerical dipoles'' - that can reproduce the near field scattered by an arbitrary particle for any (near- or far-field) excitation.

The GPM of the dipole set is determined numerically by solving an inverse problem relying on full-wave simulation data obtained with an external Maxwell’s equations solver. Once known, multiple scattering problems by large ensembles of particles in stratified media can be solved with a Green tensor formalism, even in cases of particles interacting in the near field of each other, of planar interfaces, or of localized light sources. In this manuscript, we describe the GPM method and analyze its performance in single and multiple scattering problems. In a last part, we generalize the method to handle particles directly in contact with interfaces by introducing the concept of "dressed" GPM, thereby firmly opening novel perspectives in modeling of nanoparticle-based complex media and metasurfaces.

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