Directional Fano Resonances at Light Scattering by a High Refractive Index Dielectric Sphere

TL;DR

This paper demonstrates experimental and theoretical evidence of directional Fano resonances in light scattering by a high refractive index dielectric sphere, revealing interference effects between electric dipolar and quadrupolar modes.

Contribution

It provides the first experimental observation of directional Fano resonances in dielectric spheres and extends the Fano theory to resonant interfering partitions.

Findings

Asymmetric Fano profiles observed in scattering intensity.

Theoretical and experimental results show perfect agreement.

Scaling invariance allows mimicking visible light scattering in microwave range.

Abstract

In this research, we report the experimental evidence of the directional Fano resonances at the scattering of a plane, linearly polarized electromagnetic wave by a homogeneous dielectric sphere with high refractive index and low losses. We observe a typical asymmetric Fano profile for the intensity scattered in, practically, any given direction, while the overall extinction cross section remains Lorentzian. The phenomenon is originated in the interference of the selectively excited electric dipolar and quadrupolar modes. The selectivity of the excitation is achieved by the proper choice of the frequency of the incident wave. Thanks to the scaling invariance of the Maxwell equations, in these experiments we mimic the scattering of the visible and near IR radiation by a nanoparticle made of common superconductor materials (Si, Ge, GaAs, GaP) by the equivalent scattering of a spherical particle of 18 mm in diameter in the microwave range. The theory developed to explain the experiments extends the conventional Fano approach to the case when both interfering partitions are resonant. The perfect agreement between the experiment and the theory is demonstrated.