Overcoming black body radiation limit in free space: metamaterial superemitter

Abstract

Here, we demonstrate that the power spectral density of thermal radiation at a specific wavelength produced by a body of finite dimensions set up in free space under a fixed temperature could be made theoretically arbitrary high, if one could realize double negative metamaterials with arbitrary small loss and arbitrary high absolute values of permittivity and permeability (at a given frequency). This result refutes the widespread belief that Planck's law itself sets a hard upper limit on the spectral density of power emitted by a finite macroscopic body whose size is much greater than the wavelength. Here we propose a physical realization of a metamaterial emitter whose spectral emissivity can be greater than that of the ideal black body under the same conditions. Due to the reciprocity between the heat emission and absorption processes such cooled down superemitter also acts as an optimal sink for the thermal radiation-the 'thermal black hole'-which outperforms Kirchhoff-Planck's black body which can absorb only the rays directly incident on its surface. The results may open a possibility to realize narrowband super-Planckian thermal radiators and absorbers for future thermophotovoltaic systems and other devices.

Radiation-enhancing reflector

“…Basically, we obtain a surface which (at its resonant frequency) is "more bright than the ideal PEC mirror", and this property holds even in the limit of the infinite planar reflector. In earlier work [1], [2] physically similar results were obtained for absorbers, which could be made "more black than the ideal black body" in its classical definition. However, the earlier results hold only for bodies of a finite size, as the necessary coupling of locally oscillating fields to far-field was made possible due to the surface curvature.…”

“…However, the earlier results hold only for bodies of a finite size, as the necessary coupling of locally oscillating fields to far-field was made possible due to the surface curvature. In that scenario [2], increasing the body size leads to decreasing the surface curvature, that is, to weaker coupling of resonant evanescent modes to free space. Here we remove this limitation by perturbing the surface.…”

Breaking the black-body limit with resonant surfaces

“…This well-known maximal power principle applied in circuits can be generalized to cover electrically sizable electromagnetic structures. The only difference is that, in the latter case, there are infinitely many channels (modes) for transferring energy; if all of them obey the conjugate-matching principle, the transferred power P is diverging [17]. In particular, the load can be replaced by a semi-infinite half-space filled with a uniaxial medium of relative constituent properties (e rt , l rt , e rn ) and the source by any dipole or multipole placed in the vicinity of the air-medium interface [18].…”

“…Several attempts to emulate the response of a black body have been made in acoustics [15] and photonics [16] with some success. However, very recently absorbing structures which break that upper limit posed by perfectly black body have been proposed [17,18], and they are based on the use of Double-Negative (DNG) uniaxial media which obey the Perfectly Matched Layer (PML) rule. That Conjugate Matched Layer (CML), as we call it, and its variants, would be the major topic of the present work, where alternative excitations are considered.…”

Conjugately-matched uniaxial metamaterials make extremely efficient absorbers, emitters, and reflectors

“…This well-known maximal power principle applied in circuits can be generalized to cover electrically sizable electromagnetic structures. The only difference is that in the latter case there are infinitely many channels (modes) for transferring energy; if all of them obey the conjugate-matching principle, the tranferred power P is diverging [1]. In particular, the load can be replaced by a semi-infinite halfspace filled with a uniaxial medium of relative constituent properties (ε rt , μ rt , ε rn ) and the source by any dipole or multipole placed in the vicinity of the interface [2].…”