Giant In-Particle Field Concentration and Fano Resonances at Light Scattering by High-Refractive Index Particles

TL;DR

This paper analytically investigates light scattering by high-refractive-index particles, revealing giant internal field concentrations and Fano resonances resulting from overlapping Mie modes, with explicit formulas derived for these phenomena.

Contribution

It provides a detailed analytical framework for understanding and quantifying giant field enhancements and Fano resonances in high-index particle scattering without relying on fitting.

Findings

Giant electromagnetic energy concentration within high-index particles.

Fano resonance profiles characterized by explicit parameters.

Outer scattered field approaches a universal profile as index increases.

Abstract

A detailed analytical inspection of light scattering by a particle with high refractive index m+i\kappa and small dissipative constant \kappa is presented. We have shown that there is a dramatic difference in the behavior of the electromagnetic field within the particle (inner problem) and the scattered field outside it (outer problem). With an increase in m at fix values of the other parameters, the field within the particle asymptotically converges to a periodic function of m. The electric and magnetic type Mie resonances of different orders overlap substantially. It may lead to a giant concentration of the electromagnetic energy within the particle. At the same time, we demonstrate that identical transformations of the solution for the outer problem allow to present each partial scattered wave as a sum of two partitions. One of them corresponds to the m-independent wave, scattered by a perfectly reflecting particle and plays the role of a background, while the other is associated with the excitation of a sharply-m-dependent resonant Mie mode. The interference of the partitions brings about a typical asymmetric Fano profile. The explicit expressions for the parameters of the Fano profile have been obtained "from the first principles" without any additional assumptions and/or fitting. In contrast to the inner problem, at an increase in m the resonant modes of the outer problem die out, and the scattered field converges to the universal, m-independent profile of the perfectly reflecting sphere. Numerical estimates of the discussed effects for a gallium phosphide particle are presented.