Scattering at Space-Time Interfaces between Dispersive Media

TL;DR

This paper develops a comprehensive frequency transition theory for electromagnetic scattering at moving interfaces between dispersive media, revealing how dispersion alters wave dynamics and scattering channels.

Contribution

It introduces a general nonlinear frequency transition framework that accounts for dispersion, extending existing models to realistic, dispersive materials with complex resonances.

Findings

Dispersion reshapes the space-time scattering landscape.

Resonant dispersion and negative-index branches reorganize scattering channels.

Closed-form scattering coefficients derived for two-wave scattering in dispersive media.

Abstract

Dynamic modulation of material properties in space and time enables powerful control over wave propagation, yet existing theories largely rely on idealized, nondispersive models. In realistic media, frequency dispersion can strongly reshape wave dynamics, especially near resonances in highly dispersive platforms such as epsilon-near-zero materials. Here, we develop a general frequency transition theory for electromagnetic scattering at moving interfaces between dispersive media. From phase continuity, we derive nonlinear frequency transition relations and show that dispersion fundamentally reshapes the space-time scattering landscape, enabling additional propagating solutions with no counterpart in nondispersive systems. Applied to Drude, Lorentz and double-Drude media, the theory reveals how resonant dispersion, material loss and negative-index branches reorganize the scattering channels. For the two-wave scattering class, we further introduce a mixed-domain formulation that combines time-domain interface kinematics with frequency-domain constitutive relations, yielding closed-form scattering coefficients. These results establish a unified framework for dispersive space-time scattering and open opportunities for dispersion-based transition engineering in realistic materials.