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Incandescent sources such as hot membranes and globars are widely used for mid-infrared spectroscopic applications. The emission properties of these sources can be tailored by means of resonant metasurfaces: control of the spectrum, polarization, and directivity have been reported. For detection or communication applications, fast temperature modulation is desirable but is still a challenge due to thermal inertia. Reducing thermal inertia can be achieved using nanoscale structures at the expense of a low absorption and emission cross-section. Here, we introduce a metasurface that combines nanoscale heaters to ensure fast thermal response and nanophotonic resonances to provide large monochromatic and polarized emissivity. The metasurface is based on platinum and silicon nitride and can sustain high temperatures. We report a peak emissivity of 0.8 and an operation up to 20 MHz, six orders of magnitude faster than commercially available hot membranes.

Light emission by ensembles of emitters can be tailored using resonators such as cavities or plasmonic antennas. While concepts such as field enhancement, Purcell effect, and quenching can be used to understand the interplay between a two‐level system and a resonator, they fail to account for light emission by ensembles of emitters. Recent experiments reporting light emission by thermalized molecules, quantum dots, and hot electrons excited optically or electrically are reviewed. It is shown that the local Kirchhoff's law provides a unified framework to discuss photoluminescence, electroluminescence, and thermal radiation by ensembles of thermalized emitters coupled to resonators.

We introduce thermal metallo-dielectric metasurfaces as mid IR sources. The emitter is a lossy metal. The spectral and angular emission is controlled using a periodic array of high refractive dielectric resonators. We introduce a design that allows to control independently the emission bandwidth and the angular aperture while ensuring a large emissivity. To validate the concept, we fabricated and characterized a metasurface, showing a good agreement with the theory.

We study light absorption by a dipolar absorber in a given environment, which can be a nanoantenna or any complex inhomogeneous medium. From rst-principle calculations, we derive an upper bound for the absorption, which decouples the impact of the environment from the one of the absorber. Since it is an intrinsic characteristic of the environment regardless of the absorber, it provides a good gure of merit to compare the ability of dierent systems to enhance absorption. We show that, in the scalar approximation, the relevant parameter is not the eld enhancement but the ratio between the eld enhancement and the local density of states. Consequently, a plasmonic structure supporting hot spots is not necessarily the best choice to enhance absorption. We also show that our theoretical results can be applied beyond the scalar approximation and the plane-wave illumination.

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