Journal
ACS PHOTONICS
Volume 6, Issue 11, Pages 2607-2611Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsphotonics.9b00922
Keywords
midinfrared; absorber; perfect absorber; thermal radiation; thermal emission; large area
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Funding
- National Science Foundation (NSF) [ECCS-1750341]
- Department of Energy (DOE) [DE-NE0000743]
- U.S. Army Research Office (ARO) [W911NF-17-10351]
- Kavli Institute for Bionano Science and Technology at Harvard
- National Science Foundation under NSF ECCS Award [1541959]
- NSF through the UW-Madison Materials Research Science and Engineering Center [DMR-1720415]
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Engineered optical absorbers are of substantial interest for applications ranging from stray light reduction to energy conversion. We demonstrate a large-area (centimeter-scale) metamaterial that features near-unity frequency-selective absorption in the mid-infrared wavelength range. The metamaterial comprises a self-assembled porous structure known as an inverse opal, here made of silica. The structure's large volume fraction of voids, together with the vibrational resonances of silica in the mid-infrared spectral range, reduce the metamaterial's refractive index to close to that of air and introduce considerable optical absorption. As a result, the frequency-selective structure efficiently absorbs incident light of both polarizations even at very oblique incidence angles. The absorber remains stable at high temperatures (measured up to similar to 900 degrees C), enabling its operation as a frequency-selective thermal emitter. The excellent performance of this absorber/emitter and ease of fabrication make it a promising surface coating for passive radiative cooling, laser safety, and other large-area applications.
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