Quasinormal mode as a foundational framework for all electromagnetic Fano resonances

TL;DR

This paper introduces an ab initio Maxwellian approach using quasinormal modes to analytically describe Fano resonances in electromagnetic systems, providing explicit formulas for the Fano parameter and validating them experimentally.

Contribution

It presents a novel analytical framework based on quasinormal modes for describing Fano line shapes in light scattering, moving beyond phenomenological models.

Findings

Derived an explicit analytical formula for the Fano parameter q.

Validated the formula across various electromagnetic systems.

Showed that each quasinormal mode inherently exhibits a Fano profile.

Abstract

Fano profiles are observed across various fields of wave physics. They emerge from interference phenomena and are quantified by the asymmetry parameter q. In optics, q is usually considered as a phenomenological coefficient obtained by fitting experimental or numerical data. In this work, we introduce an ab initio Maxwellian approach using quasinormal modes to analytically describe line shapes in light scattering problems. We show that the response of each individual quasinormal mode inherently exhibits a Fano profile and derive an explicit analytical formula for the Fano parameter. Experimental and numerical validations confirm the formula's accuracy across a broad spectrum of electromagnetic systems. The general expression for q opens new possibilities for fine-tuning and optimizing spectral line shapes in electromagnetism.