Incandescent temporal metamaterials

Abstract

Regarded as a promising alternative to spatially shaping matter, time-varying media can be seized to control and manipulate wave phenomena, including thermal radiation. Here, based upon the framework of macroscopic quantum electrodynamics, we elaborate a comprehensive quantum theoretical formulation that lies the basis for investigating thermal emission effects in time-modulated media. Our theory unveils unique physical features brought about by time-varying media: nontrivial correlations between fluctuating electromagnetic currents at different frequencies and positions, thermal radiation overcoming the black-body spectrum, and quantum vacuum amplification effects at finite temperature. We illustrate how these features lead to striking phenomena and innovative thermal emitters, specifically, showing that the time-modulation releases strong field fluctuations confined within epsilon-near-zero (ENZ) bodies, and that, in turn, it enables a narrowband (partially coherent) emission spanning the whole range of wavevectors, from near to far-field regimes.

Review on the Scientific and Technological Breakthroughs in Thermal Emission Engineering

“…469 Building upon this basis, it has been recently demonstrated that a proper treatment of the interaction Hamiltonian paves the way for a comprehensive theoretical framework to bridge two fundamental and currently very active areas of research in the fields of nanophotonic engineering and physics, namely, time-varying media and thermal emission. 73 ■ TIME-DEPENDENT THERMAL EMISSION:…”

New Horizons in Near-Zero Refractive Index Photonics and Hyperbolic Metamaterials

“…Temporal modulation is capable of releasing these fields, forming the dual of a spatial grating, which consists of a narrowband peak fixed at a given frequency, but whose radiation scans all wave-vectors, from near to far fields. 213…”

“…Time-modulation of the refractive index breaks key assumptions in the usual form of the fluctuation dissipation theorem and Kirchhoff’s law, which form the basis of thermal emitters. Therefore, while thermal fluctuating currents are typically uncorrelated in frequency and space for conventional thermal emitters, time modulation leads to secondary currents that are correlated in frequency and space, opening the door to thermal emission with enhanced coherence and nontrivial photon correlations . Furthermore, energy can be either pumped into a material or retracted from it as it is modulated in time, enabling “active” thermal emitters radiating outside the blackbody spectrum, and acting as heat engines .…”

“…Therefore, while thermal fluctuating currents are typically uncorrelated in frequency and space for conventional thermal emitters, time modulation leads to secondary currents that are correlated in frequency and space, opening the door to thermal emission with enhanced coherence and nontrivial photon correlations. 213 Furthermore, energy can be either pumped into a material or retracted from it as it is modulated in time, enabling "active" thermal emitters radiating outside the blackbody spectrum, 213 and acting as heat engines. 214 Thermal emission from NZI bodies is particularly sensitive to time modulation.…”

“…For example, since the near-field of a fluctuating current scale as E NF ∼ 1/(4πε r 3 ), ENZ bodies support very strong thermal fields within them. Temporal modulation is capable of releasing these fields, forming the dual of a spatial grating, which consists of a narrowband peak fixed at a given frequency, but whose radiation scans all wave-vectors, from near to far fields …”