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  • Open Access

Quasinormal modes of Floquet media slabs

Benjamin Vial*

Richard V. Craster†

  • Department of Mathematics, UMI 2004 Abraham de Moivre-CNRS, Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, United Kingdom

  • *Contact author: b.vial@imperial.ac.uk
  • †Contact author: r.craster@imperial.ac.uk
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Phys. Rev. B 112, 214201 – Published 1 December, 2025

DOI: https://doi.org/10.1103/xxnd-7d55

Abstract

Exploiting non-Hermitian wave-matter interactions in time-modulated media to enable the dynamic control of electromagnetic waves requires advanced theoretical tools. In this article we bridge concepts from photonic quasinormal modes (QNMs) and time-varying metamaterials providing the foundation for designing dynamic optical devices with prescribed scattering properties. Establishing the QNM framework for slabs with time-periodic permittivity, and solving the associated nonlinear eigenvalue problem, allows us to derive the QNM expansion capturing the resonant features of the system. This reduced-order model enables highly efficient computation of scattered fields while revealing insight into how modulation couples to resonant modes, creating tailored gain-loss engineering. Our approach is validated through numerical experiments on time-modulated systems, and we design strategies to engineer tailored excitations selectively amplifying or suppressing specific modal contributions.

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Phys. Rev. B 112, 214201– Published 1 December, 2025
  • Received 3 July 2025
  • Revised 9 October 2025
  • Accepted 7 November 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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