Amplified Emission by Atoms and Lasing in Photonic Time Crystals

TL;DR

This paper explores how photonic time crystals can amplify light emission through time-modulated media, revealing new effects like exponential amplification, linewidth narrowing, and proposing tunable PTC lasers.

Contribution

It provides a comprehensive classical and quantum analysis of emission in PTCs, demonstrating amplification mechanisms and introducing the concept of tunable PTC lasers.

Findings

Radiation is exponentially amplified at the momentum gap.

Atomic decay rate vanishes at the band edge.

Linewidth narrows over time and is centered in the momentum gap.

Abstract

Photonic Time Crystals (PTCs) - dielectric media with their refractive index modulated periodically in time, offer new opportunities in photonics arising from time reflections and momentum bandgaps. Here, we study the emission of light from a radiation source inside a PTC. We solve the general classical and quantum mechanical models of emission in a temporally-varying medium, and find that radiation is always exponentially amplified when associated with the momentum gap, whether initiated by a macroscopic source, an atom, or by vacuum fluctuations, drawing the amplification energy from the modulation. The radiation linewidth becomes narrower as time advances, and is centered in the middle of the momentum gap. We calculate the spontaneous decay rate of an atom embedded in a PTC and show that it vanishes at the band edge due to low density of photonic states. Finally, we propose the concept of nonresonant tunable PTC lasers.