Cascades of Fano resonances in light scattering by dielectric particles

Abstract

Fano lineshapes are fundamental spectroscopic signatures that quantitatively characterize the structural and dynamic properties of physical objects, from nuclei to three-dimensional solids and liquids. The study of cascades of Fano resonances is a fresh approach to the classical problem that greatly expands our knowledge and the scope of practical applications. Here it is demonstrated that in solid state physics cascades of Fano resonance can be considered as a general property of light scattering by dielectric particles with the Mie and Fabry-Perot manifold of narrow photonic eigenmodes. A general picture of Fano resonance cascades in the spectra of all basic elementary scatterers (spheres, cylinders, rings, split rings, rectangular cuboids) is presented. For rings, split rings, and cuboids, the scattering spectrum is divided into separate spectral regions, which begin with a broad transverse resonance of the Lorentz-type or Fano-type lineshape, genetically related to the modes of the disk that generates the ring, and continue with a gallery of longitudinal modes with exponentially increasing Q factors. The alternation of a cascade of transverse modes in a strict sequence of Lorentz-Fano-Lorentz-Fano-… is shown theoretically, as well as experimentally in the case of a ring. This picture opens the door to new fundamental phenomena and extended functionality of dielectric elementary scatterers due to the highly asymmetric controllable shape of the Fano line, periodically repeating in the scattering spectrum.