Alexandre Baron
University of Bordeaux
Alexandre Baron is an assistant Professor at the University of Bordeaux in France and conducts his research at the Centre de Recherche Paul Pascal. His expertise is in theoretical and experimental optics and currently collaborates closely with nanochemists and soft-matter physical chemists to study the optical properties of self-assembled composite materials. He has worked in the past at the Institute of Optics in Paris and at Duke University at the Center for Metamaterials and Integrated Plasmonics. His research interests are in nonlinear metamaterials and plasmonics, self-assembled metamaterials and disorder in photonic crystal waveguieds.
We present spherical clusters, composed of spherical dielectric or metallic inclusions, as a new kind of efficient and isotropic Huygens sources. The clusters considered act as nanoantennas in the visible or near infrared... [ view full abstract ]
We present spherical clusters, composed of spherical dielectric or metallic inclusions, as a new kind of efficient and isotropic Huygens sources. The clusters considered act as nanoantennas in the visible or near infrared domain, and exhibit highly asymmetrical scattering resulting from interferences between their optically induced modes. We demonstrate overlapped electric and magnetic resonances in our structure, giving rise to high forward scattering on resonance. We propose designs of broadband Huygens sources. In contrast to the path commonly followed in the literature [1], our approach to obtain such sources relies on the engineering of the refractive index of the effective particle rather than its geometrical shape [2]. Figure 1(a-c) are examples of several cluster realizations of different nature that show overlapped electric and magnetic multipolar behaviors and the corresponding portion of forward-scattered energy under plane wave illumination (d-f).
We show that clusters may also serve as building blocks for metasurfaces applications. We investigate their possible uses in high transmittance phase-control devices, and in thin absorber metalattices. Full wave numerical simulations show that arrays of silicon clusters can be used to shape the wavefront of a transmitted wave in the near infrared (see Fig. 2(a)). By tuning the size of the clusters or on the surface fill-fraction of the metasurface, the phase of the transmitted wave can be tuned from 0 to 2π while maintaining high transmission. By exploiting the generalized Kerker conditions involving quadrupolar resonances, we also show that our Huygens sources can be exploited to build perfect absorbers. These devices are angle-independent resonant systems that absorb close to 100% of incoming light (see Fig. 2(b)).
From an experimental point of view, clusters are particularly well-suited to bottom-up fabrication and self-assembly. They can be synthetized by making emulsions of two immiscible phases, one of which contains the nanoparticle inclusions. Therefore, they offer an alternative to the classical lithographically fabricated Huygens meta-atoms and can be made in large volumes. Examples of such synthesized particles will be shown.
[1] Decker, M., et al. (2015), Advanced Optical Materials, 3(6), 813-820.
[2] Dezert, R., et al. (2017), Physical Review B, 96(18), 180201.
Photonic & plasmonic nanomaterials , Optical properties of nanostructures , Optics and transport on 2D materials
