Near-complete violation of detailed balance in thermal radiation

Zhu, Linxiao; Fan, Shanhui

doi:10.1103/physrevb.90.220301

Cited by 197 publications

(138 citation statements)

References 52 publications

(54 reference statements)

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“…This law is valid provided that the emitter is in local thermodynamic equilibrium at a uniform temperature T and provided that the emitting medium is reciprocal. The fate of Kirchhoff law for nonreciprocal materials has been studied recently [32,33].…”

Section: Introductionmentioning

confidence: 99%

Light Emission by Nonequilibrium Bodies: Local Kirchhoff Law

et al. 2018

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The goal of this paper is to introduce a local form of Kirchhoff law to model light emission by nonequilibrium bodies. While absorption by a finite-size body is usually described using the absorption cross section, we introduce a local absorption rate per unit volume and also a local thermal emission rate per unit volume. Their equality is a local form of Kirchhoff law. We revisit the derivation of this equality and extend it to situations with subsystems in local thermodynamic equilibrium but not in equilibrium between them, such as hot electrons in a metal or electrons with different Fermi levels in the conduction band and in the valence band of a semiconductor. This form of Kirchhoff law can be used to model (i) thermal emission by nonisothermal finite-size bodies, (ii) thermal emission by bodies with carriers at different temperatures, and (iii) spontaneous emission by semiconductors under optical (photoluminescence) or electrical pumping (electroluminescence). Finally, we show that the reciprocity relation connecting light-emitting diodes and photovoltaic cells derived by Rau is a particular case of the local Kirchhoff law.

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Section: Introductionmentioning

confidence: 99%

Light Emission by Nonequilibrium Bodies: Local Kirchhoff Law

et al. 2018

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“…Over the years, a few groups have pointed out that by breaking reciprocity, we may be able to overcome these challenges (12)(13)(14), as illustrated in Fig. 1B.…”

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Breaking temporal symmetries for emission and absorption

Hadad

Soric

Alù

2016

Proc. Natl. Acad. Sci. U.S.A.

257

177

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Time-reversal symmetries impose stringent constraints on emission and absorption. Antennas, from radiofrequencies to optics, are bound to transmit and receive signals equally well from the same direction, making a directive antenna prone to receive echoes and reflections. Similarly, in thermodynamics Kirchhoff's law dictates that the absorptivity and emissivity are bound to be equal in reciprocal systems at equilibrium, e(ω, θ) = a(ω, θ), with important consequences for thermal management and energy applications. This bound requires that a good absorber emits a portion of the absorbed energy back to the source, limiting its overall efficiency. Recent works have shown that weak time modulation or mechanical motion in suitably designed structures may largely break reciprocity and time-reversal symmetry. Here we show theoretically and experimentally that a spatiotemporally modulated device can be designed to have drastically different emission and absorption properties. The proposed concept may provide significant advances for compact and efficient radiofrequency communication systems, as well as for energy harvesting and thermal management when translated to infrared frequencies.

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“…Both Kirchhoff's and Planck's treatments explicitly make two assumptions: (i) The optical properties of the object are reciprocal (e.g., excluding Faraday rotation); (ii) diffraction is neglected, presuming objects much larger than a wavelength and using ray rather than wave optics. It is, however, now known that such a directional radiation law is not correct for nonreciprocal systems (1,7), and nanophotonic structures for the control of thermal radiation (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) can have feature sizes much smaller than the wavelength. Given the fundamental thermodynamic importance and the technological relevance of radiation laws, we need to understand just what are the valid laws that cover nonreciprocal behavior and subwavelength structures and whether there are some deeper universal laws for all linear optical systems.…”

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confidence: 99%

Universal modal radiation laws for all thermal emitters

Miller

Zhu

Fan

2017

Proc. Natl. Acad. Sci. U.S.A.

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112

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We derive four laws relating the absorptivity and emissivity of thermal emitters. Unlike the original Kirchhoff radiation law derivations, these derivations include diffraction, and so are valid also for small objects, and can also cover nonreciprocal objects. The proofs exploit two recent approaches. First, we express all fields in terms of the mode-converter basis sets of beams; these sets, which can be uniquely established for any linear optical object, give orthogonal input beams that are coupled one-by-one to orthogonal output beams. Second, we consider thought experiments using universal linear optical machines, which allow us to couple appropriate beams and black bodies. Two of these laws can be regarded as rigorous extensions of previously known laws: One gives a modal version of a radiation law for reciprocal objects-the absorptivity of any input beam equals the emissivity into the "backward" (i.e., phase-conjugated) version of that beam; another gives the overall equality of the sums of the emissivities and the absorptivities for any object, including nonreciprocal ones. The other two laws, valid for reciprocal and nonreciprocal objects, are quite different from previous relations. One shows universal equivalence of the absorptivity of each mode-converter input beam and the emissivity into its corresponding scattered output beam. The other gives unexpected equivalences of absorptivity and emissivity for broad classes of beams. Additionally, we prove these orthogonal mode-converter sets of input and output beams are the ones that maximize absorptivities and emissivities, respectively, giving these beams surprising additional physical meaning.Kirchhoff radiation laws | thermal radiation | optical modes | solar energy conversion | mode conversion R adiation laws relating the absorptivity and emissivity of an object are at the core of the thermal physics of radiation and are particularly interesting for understanding limits to efficiency of solar energy conversion (e.g., refs. 1 and 2), for example. The core relation is Kirchhoff's radiation law (3-6), which equates the absorptivity and emissivity of a surface. This law is often extended to a "directional" version, which equates the absorptivity of a given direction of input beam and the emissivity into the opposite or "reversed" direction. Typical textbook approaches (5, 6) to the directional law trace back to Planck's rederivation (4) of Kirchhoff's approach (3). Both Kirchhoff's and Planck's treatments explicitly make two assumptions: (i) The optical properties of the object are reciprocal (e.g., excluding Faraday rotation); (ii) diffraction is neglected, presuming objects much larger than a wavelength and using ray rather than wave optics. It is, however, now known that such a directional radiation law is not correct for nonreciprocal systems (1, 7), and nanophotonic structures for the control of thermal radiation (8-22) can have feature sizes much smaller than the wavelength. Given the fundamental thermodynamic importance and the technological relevan...

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Near-complete violation of detailed balance in thermal radiation

Cited by 197 publications

References 52 publications

Light Emission by Nonequilibrium Bodies: Local Kirchhoff Law

Light Emission by Nonequilibrium Bodies: Local Kirchhoff Law

Breaking temporal symmetries for emission and absorption

Universal modal radiation laws for all thermal emitters

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