We show that weakly dissipating dielectric spheres made of materials such as glass, quartz, etc. can support high order Fano resonances associated with internal Mie modes. These resonances, happening for specific values of the size parameter, yield field-intensity enhancement factors on the order of 104–107, which can be directly obtained from analytical calculations. Associated to these “super-resonances”, we analyze the emergence of magnetic nanojets with giant magnetic fields, which might be attractive for many photonic applications.

Hyperbolic Metamaterials are artificially engineered materials whose optical properties can be specifically tailored to manifest an extremely high level of anisotropy. Due to this remarkable anisotropy they represent a unique opportunity to realize effective bulk meta-structure with extraordinary optical properties in the visible range. A simultaneous dielectric singularity in the in plane permittivity, with respect to the propagation direction, has to lead to a complete sign inversion of the same permittivity for that specific visible frequency. Such a drastic phase change has been theoretically highlighted in the past as the major challenge to be overcome in order to unlock many remarkable optical properties not present artificial optical systems. In this paper we experimentally demonstrate the realization of a metal-dielectric multilayer structure showing an inversion point of coexisting anisotropies at a specified wavelength in the visible range, rising from the particular design and fabrication process. Theoretical models and numerical simulations are in very good agreement with experimental data. Ellipsometrical experiments and optical modeling demonstrate the drastic type I/type II transition. Supercollimation effect has been achieved at the inversion point of the coexisting extreme anisotropies, whereas at the epsilon near zero and pole frequency the perfect lens behavior has been observed.

4 pagesInternational audienceWe report on the broadband resonant energy transfer processes observed in dye doped gold nanoshells, consisting of spherical particles with a dielectric core (SiO2) covered by a thin gold shell. The silica core has been doped with rhodamine B molecules in order to harness a coherent plasmon-exciton coupling between chromophores and plasmonic shell. This plasmon-exciton interplay depends on the relative spectral position of their bands. Here, we present a simultaneous double strong coupling plasmon-exciton and exciton-plasmon. Indeed, experimental observations reveal of a transmittance enhancement as function of the gain in a wide range of optical wavelengths (about 100 nm), while scattering cross sections remains almost unmodified. These results are accompanied by an overall reduction of chromophore fluorescence lifetimes that are a clear evidence of nonradiative energy transfer processes. The increasing of transmission in the range of 630-750 nm is associated with a striking enhancement of the extinction cross-section in the 510-630 nm spectral region. In this range, the system assumes super-absorbing features. This double behavior, as well as the broadband response of the presented system, represents a promising step to enable a wide range of electromagnetic properties and fascinating applications of plasmonic nanoshells as building blocks for advanced optical materials

Inherent optical losses of plasmonic materials represent a crucial issue for optoplasmonics, whereas the realization of hierarchical plasmonic nanostructures implemented with gain functionalities is a promising and valuable solution to the problem. Here we demonstrate that porous silica capsules embedding gold nanoparticles (Au NPs) and fabricated at a scale intermediate between the single plasmonic nanostructure and bulk materials show remarkable form–function relations. At this scale, in fact, the plasmon–gain interplay is dominated by the location of the gain medium with respect to the spatial distribution of the local field. In particular, the hollow spherical cavities of these structures allow regions of uniform plasmonic field where the energy transfer occurring between chromophoric donors and the surrounding plasmonic acceptors gives rise to a broadband attenuation of losses.