Revealing Fano Combs in Directional Mie Scattering

Abstract

The constructive interference of light reflecting on the inner surface of a dielectric sphere results in a rich Mie scattering spectrum. Each resonance can be understood through a quantum-mechanical analogy, while the structure of the full spectrum is predicted to be a series of Fano resonances. However, the overlap of all the different modes results in such a complex spectrum that an intuitive understanding of the full, underlying structure is still missing. Here we present a directional Mie spectrum obtained by selecting a particular polarization and direction of the scattering of levitating water droplets. We find a significantly simplified spectrum organized in distinct, consecutive Mie Fano Combs composed of equidistant resonances that smoothly evolve from wide Lorentzians into sharp Fano profiles. We then fully explain all these characteristics by expanding on the quantum-mechanical analogy. This makes it possible to understand Mie spectra intuitively without the need for computational simulations.