Crossing the light line

TL;DR

This paper explores the behavior of Bloch waves in moving gratings near light speed, revealing dispersion rotation, pulse inflation, and propagation reversal, with models that accurately describe these phenomena.

Contribution

It introduces a constant refractive index model and a refined 4-wave model to analyze Bloch waves in superluminal gratings, providing new insights into their dispersion and pulse dynamics.

Findings

Bloch waves' dispersion rotates through 360 degrees near light speed

Pulse amplitude suddenly inflates when a luminal grating is activated

Propagation direction of light pulses can reverse in moving gratings

Abstract

We ask the question 'what happens to Bloch waves in gratings synthetically moving at near the speed of light?'. First we define a constant refractive index (CRI) model in which Bloch waves remain well defined as they break the light barrier, then show their dispersion rotating through 360 degrees from negative to positive and back again. Next we introduce the effective medium approximation (EMA) then refine it into a 4-wave model which proves to be highly accurate. Finally using the Bloch waves to expand a pulse of light we demonstrate sudden inflation of pulse amplitude combined with reversal of propagation direction as a luminal grating is turned on.