Exact theory and approximations for optical resonators in a changing external medium

Almousa, S. F. and Muljarov, E. A. ORCID: https://orcid.org/0000-0002-2878-4148 2023. Exact theory and approximations for optical resonators in a changing external medium. Physical Review B 107 (8) , L081401. 10.1103/PhysRevB.107.L081401

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Abstract

Finding reliably and efficiently the spectrum of the resonant states of an optical system under varying parameters of the medium surrounding it is a technologically important task, primarily due to various sensing applications. Computationally, it presents, however, a fundamental challenge owing to the nature of the eigenstates of an open system lacking completeness outside it. We solve this challenge by making a linear transformation of Maxwell's equations which maps perturbations of the surrounding medium onto effective perturbations within the system where the resonant states are complete. By treating such perturbations with a rigorous resonant-state expansion, we find the modified modes of the system for arbitrary homogeneous perturbations of the medium with any required accuracy. A numerically efficient single-mode approximation is shown to be highly accurate, as illustrated for various plasmonic nanoparticles, including gold nanospheres and silver bowtie antennas.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	American Physical Society
ISSN:	2469-9950
Date of First Compliant Deposit:	10 February 2023
Date of Acceptance:	24 January 2023
Last Modified:	09 Nov 2023 21:34
URI:	https://orca.cardiff.ac.uk/id/eprint/156870

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