Time-Varying Media and Photonic Time-Crystals
The rich physics of optical systems in time-varying media have been explored since the late 1950s when it was shown that there are mechanisms of time-reflection and refraction of waves from temporal interfaces. In the last few years, the field has received renewed attention, when one of the newly investigated systems is a “Photonic Time-Crystal”: a medium with a time-periodic change in the refractive index, a time analog to spatial crystals. Photonic time-crystals display unique light-matter interaction properties and are promising candidates for new light sources for lasing and for quantum light. However, in order to experimentally probe these systems in the optical regime, we first need a medium that can change its index of refraction sharply in the timescale of few femtoseconds.
Recently, new advancements in controlling the optical properties of “Epsilon Near Zero” materials, have made these materials prime candidates for demonstrating time-refraction and time-reflection of optical waves from time-interfaces, which are the fundamental steps towards creating the first optical photonic time-crystals.