Photonic time crystals (PTCs), materials with a dielectric permittivity that is modulated periodically in time, offer new concepts in light manipulation. We study theoretically the emission of light from a radiation source placed inside a PTC and find that radiation corresponding to the momentum bandgap is exponentially amplified, whether initiated by a macroscopic source, an atom, or vacuum fluctuations, drawing the amplification energy from the modulation. The radiation linewidth becomes narrower with time, eventually becoming monochromatic in the middle of the bandgap, which enables us to propose the concept of nonresonant tunable PTC laser. Finally, we find that the spontaneous decay rate of an atom embedded in a PTC vanishes at the band edge because of the low density of photonic states.

中文翻译：

---

光子时间晶体中的放大发射和激光。

光子时间晶体 (PTC) 是一种介电常数随时间周期性调制的材料，它为光操纵提供了新的概念。我们从理论上研究了放置在 PTC 内的辐射源的光发射，发现对应于动量带隙的辐射呈指数放大，无论是由宏观源、原子还是真空涨落引发，从调制中汲取放大能量。辐射线宽随时间变窄，最终在带隙中间变为单色，这使我们能够提出非谐振可调谐PTC激光器的概念。最后，我们发现嵌入 PTC 的原子的自发衰减率在能带边缘消失，因为光子态的密度低。