Work

Reflections on the Spatial Exponential Growth of Electromagnetic Quasinormal Modes

Year: 2025

Type: article

Abstract: A major research objective across various fields is to represent the response of open systems using quasinormal mode (QNM) expansions, akin to the treatment of normal modes in closed systems. In electromagnetism, QNM expansions effectively describe modal physics inside resonators and in their near field. However, challenges arise in the intermediate and far field, where QNM fields grow exponentially, posing mathematical issues and often being considered unphysical. How can a near‐field relevant concept lose its validity? Where does this transition occur? This perspective seeks to answer these questions by analyzing foundational concepts such as cavity perturbation theory and dissipative coupling using model problems. The analysis reveals no fundamental inconsistencies with exponential growth and sometimes yields surprising results, such as an increase in coupling coefficients between QNMs of two distant bodies as separation increases. These findings should be widely shared to prevent misunderstandings and enhance the understanding of contemporary electromagnetic QNM theories. The final section, intended for experts in electromagnetic QNMs, provides a thorough analysis of these theories.

Source: Laser & Photonics Review

DOI: 10.1002/lpor.202402133

Authors: Tong Wu, José Luis Jaramillo, Philippe Lalanne

Institutions: Centre National de la Recherche Scientifique, Université de Bordeaux, Laboratoire Photonique, Numérique et Nanosciences, Université de Bourgogne, Institut de Mathématiques de Bourgogne

Language: English

Topic: Electromagnetic Scattering and Analysis

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,880

Funder: Agence Nationale de la Recherche