Enhancement and suppression of thermal emission by a three-dimensional photonic crystal

Lin, Shawn‐Yu; Fleming, J. G.; Chow, Edmond; Bur, James A.; Choi, K. K.; Goldberg, Arnold C.

doi:10.1103/physrevb.62.r2243

Cited by 188 publications

(101 citation statements)

References 19 publications

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“…Here we experimentally demonstrate a visibly transparent thermal blackbody, based on a silica photonic crystal, using a thermophotonic approach (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). When placed on a silicon absorber under sunlight, such a blackbody preserves and even slightly enhances sunlight absorption, but reduces the temperature of the silicon absorber by as much as 13°C due to radiative cooling.…”

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confidence: 98%

Radiative cooling of solar absorbers using a visibly transparent photonic crystal thermal blackbody

Zhu

Raman

Fan

2015

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

495

351

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A solar absorber, under the sun, is heated up by sunlight. In many applications, including solar cells and outdoor structures, the absorption of sunlight is intrinsic for either operational or aesthetic considerations, but the resulting heating is undesirable. Because a solar absorber by necessity faces the sky, it also naturally has radiative access to the coldness of the universe. Therefore, in these applications it would be very attractive to directly use the sky as a heat sink while preserving solar absorption properties. Here we experimentally demonstrate a visibly transparent thermal blackbody, based on a silica photonic crystal. When placed on a silicon absorber under sunlight, such a blackbody preserves or even slightly enhances sunlight absorption, but reduces the temperature of the underlying silicon absorber by as much as 13°C due to radiative cooling. Our work shows that the concept of radiative cooling can be used in combination with the utilization of sunlight, enabling new technological capabilities.radiative cooling | thermal radiation | photonic crystal | solar absorber T he universe, at a temperature of 3 K, represents a significant renewable thermodynamic resource: it is the ultimate heat sink. Over midinfrared wavelengths, in particular between 8 and 13 μm, Earth's atmosphere is remarkably transparent to electromagnetic radiation. This wavelength range coincides with the peak wavelength of thermal radiation from terrestrial structures at typical ambient temperatures. Thus, a sky-facing terrestrial object can have radiative access to the universe. Exploiting this radiative access has led to the demonstration of radiative cooling (1-7), as well as proposals for direct electric power generation from thermal radiation of terrestrial objects (8).Whereas historically radiative cooling was largely developed for night-time applications (1-6, 9-13), recent works have achieved daytime radiative cooling (7,14). In particular, it was shown that the radiative cooling to below ambient air temperature can be achieved (7), with a photonic structure that reflects almost all incident sunlight and simultaneously emits significant thermal radiation in the midinfrared. Such a structure, being a near-perfect solar reflector, makes no use of incident sunlight. On the other hand, in many applications, including solar cells (15) and outdoor structures (16), the utilization of sunlight through absorption is intrinsic for either operational or aesthetic considerations, but the heating associated with sunlight absorption is undesirable. For these applications, lowering operating temperatures via radiative cooling is only viable if one can simultaneously preserve the absorption of sunlight.Here we experimentally demonstrate a visibly transparent thermal blackbody, based on a silica photonic crystal, using a thermophotonic approach (17-30). When placed on a silicon absorber under sunlight, such a blackbody preserves and even slightly enhances sunlight absorption, but reduces the temperature of the silicon absorber by as m...

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mentioning

confidence: 98%

Radiative cooling of solar absorbers using a visibly transparent photonic crystal thermal blackbody

Zhu

Raman

Fan

2015

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

495

351

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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.

108

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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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“…In recent years, significant efforts have been devoted to the use of engineered photonic structures, including photonic crystals [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], optical antennas [27][28][29] and metamaterials [30][31][32], for the control of thermal radiation properties. Photonic structures can exhibit thermal radiation properties that are significantly different from naturally occurring materials.…”

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confidence: 99%