Abstract
We analyze the radiative power emitted by a semi-infinite medium and absorbed by a flat film located in its vicinity. In the near-field regime, if the film is thin enough, the surface waves at the rear interface of the film can contribute to the heat transfer. As a result, the absorbed power can be enhanced farther from the front surface. In the near-to-far field transition regime, temporal coherence of thermal radiation and the associated interferences can be used to shape the spectrum of the transferred radiative heat flux by selecting approriate geometrical parameters. These results highlight possibilities to control both the location where the radiative power is absorbed in the film and the spectral distribution, which are of paramount importance for applications such as near-field thermophotovoltaics.
Highlights
Because Planck’s blackbody spectral distribution of thermal radiation does not take the contribution of evanescent waves into account, it is not valid anymore in the near-field, where radiative transfer via tunneling of evanescent waves is dominant
These results highlight possibilities to control both the location where the radiative power is absorbed in the film and the spectral distribution, which are of paramount importance for applications such as near-field thermophotovoltaics
In the case of two planar parallel bodies separated by a subwavelength distance, this leads to a large increase of the radiative heat flux[1,2] and, in the particular case of materials supporting surface phonon-polaritons (SPhPs) or surface plasmon-polaritons (SPPs), to the apparition of resonances in the spectrum of thermal radiation.[3]
Summary
Another group[23,24] studied the variation of the penetration depth inside hyperbolic metamaterials, where the impact of frustrated modes on the spatial absorption is significant. These modes are propagative inside the absorber, so they are expected to have a larger penetration depth than surface modes. It was observed for the case of two semi-infinite media that another regime can appear when the distance separating the bodies is close to the value of the characteristic wavelength of thermal radiation. We investigate the transition between the near-field and the far-field regimes, observing how interferences can affect the spectrum of thermal radiation and the total radiative power transferred from the semi-infinite emitter to the film
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