Spatiotemporal Co-reflection with Spacetime Discontinuities at Moving Interfaces

TL;DR

This paper introduces a novel spatiotemporal interface mechanism enabling negative refraction and backscattering suppression, leading to a nonreciprocal flat lens for electromagnetic waves.

Contribution

It demonstrates that spatiotemporal co-reflection can occur at moving interfaces under specific conditions, advancing the design of time-varying metamaterials.

Findings

Negative refraction with no backscattering achieved at moving interfaces.

Spatiotemporal co-reflection is possible under oblique incidence with certain velocities.

Proposed a nonreciprocal flat lens leveraging this mechanism.

Abstract

The control of reflection and refraction at interfaces using engineered media is central to numerous optical technologies, with negative refraction and the suppression of backscattering representing two prominent research frontiers. In this work, we demonstrate that an effective negative refraction accompanied by an absence of backscattering can be realized at a moving spatiotemporal interface when temporal and spatial reflections occur concurrently. While such spatiotemporal co-reflection is prohibited in one-dimensional linear dispersive media, we show that it becomes permissible under oblique incidence within a specific range of traveling-wave modulation velocities. Leveraging this mechanism, we propose a spatiotemporal flat lens capable of nonreciprocal electromagnetic wave focusing. These findings provide a framework for developing advanced spatiotemporal metamaterials and time-varying metasurfaces.