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Proceedings Paper

Asymmetric angular-selective thermal emission
Author(s): Enas Sakr; Shailja Dhaka; Peter Bermel
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Paper Abstract

Thermal emission from blackbodies and flat metallic surfaces is non-directional, following the Lambert cosine law. However, highly directional thermal emission could be useful for improving the efficiency of a broad range of different applications, including thermophotovoltaics, spectroscopy and infra-red light sources. This is particularly true if strong symmetry breaking could ensure emission only in one particular direction. In this work, we investigate the possibility of tailoring asymmetric thermal emission using structured metasurfaces. These are built from surface grating unit elements that support asymmetric localization of thermal surface plasmon polaritons. The angular dependence of emissivity is studied using a rigorous coupled wave analysis (RCWA) of absorption, plus Kirchhoff’s law of thermal radiation. It is further validated using a direct thermal simulation of emission originating from the metal. Asymmetric angular selectivity with near-blackbody emissivity is demonstrated for different shallow blazed grating structures. We study the effect of changing the period, depth and shape of the grating unit cell on the direction angle, angular spread, and magnitude of coupled radiation mode. In particular, a periodic sawtooth structure with a period of 1.5λ and angle of 8°was shown to create significant asymmetry of at least a factor of 3. Such structures can be considered arbitrary directional sources that can be carefully patterned on metallic surfaces to yield thermal lenses with designed focal lengths, targeted to particular concentration ratios. The benefit of this approach is that it can enhance the view factor between thermal emitters and receivers, without restricting the area ratio or separation distance.

Paper Details

Date Published: 14 March 2016
PDF: 8 pages
Proc. SPIE 9743, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices V, 97431D (14 March 2016); doi: 10.1117/12.2211035
Show Author Affiliations
Enas Sakr, Purdue Univ. (United States)
Shailja Dhaka, Purdue Univ. (United States)
Peter Bermel, Purdue Univ. (United States)

Published in SPIE Proceedings Vol. 9743:
Physics, Simulation, and Photonic Engineering of Photovoltaic Devices V
Alexandre Freundlich; Laurent Lombez; Masakazu Sugiyama, Editor(s)

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