Electromagnetic Wave Trapping at the Discretized Interluminal Interface

Abstract Spatiotemporal moving interface consists of two media with different refractive indices separated by a boundary that propagates at a constant velocity. Although electromagnetic wave scatterings at the subluminal and superluminal interfaces have been well understood, how electromagnetic waves interact with the interluminal interface remains obstinate due to the breaking of phase matching and field continuity conditions at the moving boundary. Here, this problem is addressed by discretizing the moving interface into alternating spatial and temporal boundaries with larger scale than the incident wave packet. Consequently, the scattering event is discretized sequentially in a purely spatial or purely temporal boundary, thereby preserving both phase matching and field continuity conditions and enabling a closed‐form solution toward the interluminal scattering problem. The results reveal that the discretized interluminal boundary is analogous to the event horizons of black and white holes during the wave propagation, where transmitted or reflected waves become perpetually trapped at the discretized interface. These trapped waves undergo cascaded amplification and compression during propagation, resulting in a single forward‐propagating mode and an indefinite sequence of counter‐scattered modes, which can be utilized to achieve tunable and extreme field amplification and compression.