arXiv subjects

Virginie Ponsinet

Publications and source records attributed to Virginie Ponsinet.

6 recordsLinked to original sources

arXiv2023

Broadband forward scattering of light by plasmonic balls: role of multipolar interferences

Efficient and broadband forward-scattering is a property of prime importance for meta-atoms if they are to be used in self-assembled metasurfaces. Strong contenders include colloidal nanoresonators with tailored multipolar content to achieve the proper interferences that suppress back-scattering. We consider dense plasmonic balls composed of more than a hundred silver nanoinclusions. Numerical simulations provide a full understanding of the role played by multipole moments in the scattering behavior. They are fabricated using emulsion drying and characterized optically. Strong and efficient forward-scattering is demonstrated over the entire visible range. Electric and magnetic dipole resonances of equal amplitude and phase are evidenced. Such plasmonic balls could be used as meta-atoms for bottom-up metasurface applications.

physics.optics↗

arXiv2022

Effective medium description of dense clusters of plasmonic nanoparticles with spatial dispersion

We study the electromagnetic behaviour of dense, spherical clusters made of hundreds of plasmonic nanoparticules under illumination by a plane wave. Using high-precision T-matrix numerical calculations, we compute the multipolar response of clusters up to 80 nm in radius and up to 44\% in particle volume fraction. We then investigate whether it is possible to obtain an effective medium description for the clusters, taking into account weak spatial dispersion in a fully consistent way. We find that the average scattered field as well as the average inner field of the spherical cluster can be accurately reproduced by applying an extended Mie theory to an equivalent homogeneous sphere characterized by three effective parameters: an electric permittivity $\varepsilon_{\mathrm{eff}}$ and a magnetic permeability $\mu_{\mathrm{eff}}$, associated to transverse modes, and a wavevector $k_\mathrm{L}$, associated to a longitudinal mode in the sphere. Our results show that artificial magnetism arises from interparticle couplings in the dense cluster, despite inclusions not displaying any individual magnetic dipole. We also find that, although largely overlooked in the literature on metamaterials, the presence of the longitudinal mode is essential to accurately reproduce the fields of the cluster, on par with the role of artificial magnetism. Our study therefore proves that, even for high concentration in inclusions, it is possible empirically to treat a cluster of plasmonic particles as a sphere made of a spatially-dispersive homogeneous medium. This offers a practical solution facilitating the computation of electromagnetic responses of such dense random media in diverse configurations of interest for the design of metamaterials and metasurfaces.

physics.optics↗

arXiv2019

Direct retrieval method of the effective permittivity and permeability of bulk semi-infinite metamaterials by variable-angle spectroscopic ellipsometry

In this work, we present a simple method for the direct retrieval of the effective permittivity and permeability of a bulk semi-infinite metamaterial from variable-angle spectroscopic ellipsometry measurements. Starting from the well-known Fresnel equations, we derive an analytical expression in which unknown coefficients are fitted to the experimental data using a linear regression model. The effective permittivity and permeability are then determined by solving a simple system and the correct solution is selected based on physical criteria. As an example, the method is applied to the case of a self-assembled metamaterial exhibiting strong isotropic optical magnetism.

physics.optics↗

arXiv2019

Self-assembled nanostructured metamaterials

The concept of metamaterials emerged in years 2000 with the achievement of artificial structures enabling non conventional propagation of electromagnetic waves, such as negative phase velocity of negative refraction. The electromagnetic response of metamaterials is generally based on the presence of optically-resonant elements (or meta-atoms) of sub-wavelength size and well designed morphology so as to provide the desired electric and magnetic optical properties. Top-down technologies based on lithography techniques have been intensively used to fabricate a variety of efficient electric and magnetic resonators operating from microwave to visible light frequencies. However, the technological limits of the top-down approach are reached in visible light where a huge number of nanometre sized elements is required. We show here that the bottom-up fabrication route based on the combination of nanochemistry and of the self-assembly methods of colloidal physics provide an excellent alternative for the large scale synthesis of complex meta-atoms, as well as for the fabrication of 2D and 3D samples exhibiting meta-properties in visible light.

physics.optics↗

arXiv2019

High optical magnetism of dodecahedral plasmonic meta-atoms

The generation in artificial composites of a magnetic response to light comparable in magnitude with the natural electric response, may offer an invaluable control parameter for a fine steering of light at the nanoscale. In many experimental realizations however, the magnetic response of artificial meta-atoms is too weak so that there is a need for new designs with increased magnetic polarizability. Numerical simulations show that geometrical plasmonic nanostructures based on the ideal model of Platonic solids are excellent candidates for the production of strong optical magnetism in visible light. Inspired by this model, we developed a bottom-up approach to synthesize plasmonic nano-clusters made of twelve gold patched located at the center of the faces of a dodecahedron. The scattering of the electric and magnetic dipole induced by light are measured across the whole visible range. The ratio of the magnetic to electric response at resonance is found three times higher than its counterpart measured on disordered plasmonic clusters (plasmonic raspberries) of the same size. Numerical simulations confirm the experimental measurements of the magnetic response.

physics.optics↗

arXiv2016

Hierarchical self-assembly of nanoparticles for optical metamaterials

Hierarchical self-assembly arranges nanostructures at different length scales. It gradually becomes an effective method of fabricating artificial metamaterials from composite nanostructures tailored for a particular response. Hierarchical self-assembly overcomes shortcomings of "top-down" methods by significantly reducing fabrication time and making it possible to form bulk materials. Here we report an application of hierarchical self-assembly of metal nanoparticles for the creation of the first isotropic optical metamaterial with strong artificial magnetism in blue light. We have used colloidal self-assembly to create artificial "nanomolecules" that generate the desired magnetic response and microfluidic self-assembly to produce a bulk metastructure. We demonstrate that the magnetic response of the final material is accurately described by an isotropic magnetic permeability that satisfies the principle of locality. Our approach unlocks the fabrication of large volumes of composite nanomaterials. Moreover, the spatial disorder inherent to this "bottom-up" method holds the key to solving the non-locality problem. The technique can be readily extended to the future generations of low-loss optical metamaterials made of dielectric nano-blocks to bypass the limitations of optical losses associated with plasmonic resonances in noble metals.

cond-mat.mtrl-sci↗