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Efficient and intuitive modelling of electromagnetic nanoresonators and complex metasurfaces

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Controlling the interaction of light with nanoresonators is one of the spearheads of research in modern optics and photonics. Important efforts are dedicated to the design of individual nanoresonators (Mie resonators, plasmonic nanoantennas) to scatter light with tailored directionality, phase and polarization. The design is generally made by series of electromagnetic simulations realized at many incident angles, polarization and frequencies. Besides being computationally heavy, this strategy hardly brings physical insight into the problem at hand. The designed nanoresonators are then often placed in planar geometries, creating the so-called metasurfaces. The interaction of resonators with a stratified medium and between themselves can further enrich their optical properties, leading for instance to the a spectrally-selective angle-independent absorption or to controlled coupling between free-space modes and guided modes. These metasurfaces can sometimes be made by bottom-up approaches, relying on colloidal chemistry and self-assembly techniques. Theoretically predicting the optical properties of complex, disordered metasurfaces are however remained elusive up to now due to the difficulty to consider simultaneously the coherent phenomena occurring at the level of the individual nanoparticle (nano-scale) and at the level of the nanoparticle ensemble (meso-scale). In this seminar, I will present powerful numerical methods that are currently being developed in the “Light in Complex Nanostructures” group at LP2N . In a first part, I will present a formalism based on the concept of quasinormal modes that allows analysing individual nanoresonators with great physical insight and strongly reduced computational cost [1]. I will show how this formalism can be used to analyze the multipolar behavior of nanoresonators and reach designs that are tolerant to variations in frequency and incident angles [2]. In the second part, I will introduce a new numerical method that enables an efficient modeling of large, disordered ensembles of complex (non-spherical) resonators in stratified media, including in cases of strong near-field interactions [3].

[1] P. Lalanne et al., “Light interaction with photonic and plasmonic resonances”, Laser Photon. Rev. 12, 1700113 (2018).

[2] T. Wu et al., “Intrinsic multipolar contents of nanoresonators for tailored scattering”, arXiv:1907.04598 (2019).

[3] M. Bertrand et al., “Global polarizability matrix method for efficient modelling of light scattering by dense ensembles of non-spherical particles in stratified media”, arXiv:1907.12823 (2019).

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