Time Circular Birefringence in Time-Dependent Magnetoelectric Media

TL;DR

This paper introduces the concept of time circular birefringence in time-dependent magnetoelectric media, revealing unique polarization effects and proposing experimental methods to observe these phenomena.

Contribution

It demonstrates the existence of time circular birefringence in axion-type media and explores its implications for polarization rotation and pulse trapping.

Findings

Degenerate modes with opposite circular polarizations in time-dependent media

Time Faraday effect causes polarization axes to rotate over time

Pulse trapping occurs when wave-vector spectrum concentrates in non-traveling-wave band

Abstract

Light traveling in time-dependent media has many extraordinary properties which can be utilized to convert frequency, achieve temporal cloaking, and simulate cosmological phenomena. In this paper, we focus on time-dependent axion-type magnetoelectric (ME) media, and prove that light in these media always has two degenerate modes with opposite circular polarizations corresponding to one wave vector $\mathbf{k}$, and name this effect "time circular birefringence" (TCB). By interchanging the status of space and time, the pair of TCB modes can appear simultaneously via "time refraction" and "time reflection" of a linear polarized incident wave at a time interface of ME media. The superposition of the two TCB modes causes the "time Faraday effect", namely the globally unified polarization axes rotate with time. A circularly polarized Gaussian pulse traversing a time interface is also studied. If the wave-vector spectrum of a pulse mainly concentrates in the non-traveling-wave band, the pulse will be trapped with nearly fixed center while its intensity will grow rapidly. In addition, we propose an experimental scheme of using molecular fluid with external time-varying electric and magnetic fields both parallel to the direction of light to realize these phenomena in practice.