Amplified emission and lasing in photonic time crystals

Abstract

Photonic time crystals – materials whose dielectric permittivity 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 photonic time crystal, and find that radiation corresponding to the momentum band gap is exponentially amplified, whether initiated by a macroscopic source, an atom, or by vacuum fluctuations, drawing the amplification energy from the modulation. The radiation linewidth becomes narrower with time, eventually shrinking to the middle of the bandgap, which enables to propose the concept of non-resonant tunable photonic time-crystal laser. Finally, we find that the spontaneous decay rate of an atom embedded in a photonic time-crystal vanishes at the band edge due to low density of photonic states.

Unidirectional edge modes in time-modulated metamaterials

“…This has been numerically observed and proved in the recent paper [49]. Interesting applications of achieving exponentially growing wave propagation in space –time-modulated media are developed in [50]. On the other hand, the modulation frequency plays an important role.…”

Superluminal k-gap solitons in photonic time-crystals with Kerr nonlinearity

“…Second, the soliton consists of two counterpropagating pulses that are simultaneously generated. The underlying physics of pair generation stems from the momentum conservation in PTCs [15,50]. Third, we see that the full electromagnetic field of soliton is oscillating at frequency and wavevector:…”

“…In fact, the gap modes of PTCs draw energy from the modulation (or lose their energy to it). The unavoidable presence of exponentially growing (and decaying) gap modes in PTCs is intimately related to causality (see intuitive explanation in [12]). In the past few years, PTCs have been drawing growing research interest [10][11][12][13][14][15][16][17][18][19][20][21], and the recent experimental progress with very large permittivity changes at few-femtosecond time scales in epsilon-near-zero materials [22][23][24][25][26][27][28] suggests that PTCs at optical frequencies will be observed in the near future.…”

Metasurface-Based Realization of Photonic Time Crystals

“…In the past few years, numerous new physical effects have been discovered based on time modulation of material properties, such as magnetless nonreciprocity [4,5], effective magnetic field for photons [6,7], synthetic dimensions [8][9][10][11], electromagnetic devices beyond physical bounds [12,13], among many others [1]. One of the major developments in this direction is the concept of photonic time crystals (PhTCs) [14,15]. PhTCs are artificial materials whose electromagnetic properties (such as permittivity or permeability) are periodically and rapidly modulated in time while remaining uniform in space.…”

“…This is in sharp contrast to wave attenuation in time occurring inside a frequency bandgap [16,17]. Recently, numerous interesting wave phenomena have been theoretically predicted in PhTCs, such as topologically nontrivial phases [8], a temporal analog of Anderson localization [18,19], amplified radiation from free electrons and atoms [15,20], etc.…”