Spectral Expansions of Response Functions and Multiple-Scattering Theory

Abstract: The first part of this talk reviews the central role of response functions in single- and multiplescattering theories of light, together with the limitations imposed by their conventional formulation in the time-harmonic regime. I will then show how spectral expansions of response functions, and the closely related theory of Quasi-Normal Modes provide a natural framework for extending these approaches to broadband excitation and transient optical phenomena. The second part of the talk focuses on Foldy-Lax multiple-scattering theory. After outlining the formalism, I will discuss some of its principal computational challenges, including efficient solution strategies and issues of numerical stability. I will then present several applications that illustrate the versatility of the method. These include the design of optical nanoantennas for tailoring the spontaneous-emission rate and radiation pattern of quantum emitters, as well as the computation of optical forces in complex scattering environments. I will conclude by discussing how optical-force calculations can serve as a sensitive benchmark for assessing the numerical stability and accuracy of multiple-scattering algorithms.
Bio: Dr. Brian Stout is a Full Professor of Physics at Aix-Marseille Université within the Institut Fresnel. He completed his Ph.D. in Physics at the State University of New York at Stony Brook, defending a thesis on neutrino mass and nuclear double beta decay. In 2006, he obtained his Habilitation à Diriger des Recherches, investigating the interaction of light with three-dimensional heterogeneous media. Dr. Stout’s research advances computational electromagnetics and multiple-scattering theory, particularly through the application of spectral expansions of response functions and quasi-normal modes. His theoretical methodologies analyze transient optical phenomena, broadband excitation, and Foldy-Lax formalisms. He applies mathematical rigor to the optimization of optical nanoantennas, the evaluation of optical forces, and the characterization of Mie resonances and localized plasmon excitations. Serving as the co-head of the CLARTE team at the Institut Fresnel from 2014 to 2022, Dr. Stout has supervised 14 doctoral dissertations.