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TECHNICAL PAPERS: Radiative Heat Transfer

Effects of Periodic Structures on the Coherence Properties of Blackbody Radiation

[+] Author and Article Information
L. Hu, A. Schmidt, A. Narayanaswamy, G. Chen

Mechanical Engineering Department, Massachusetts Institute of Technology, Cambridge, MA 02139

J. Heat Transfer 126(5), 786-792 (Nov 16, 2004) (7 pages) doi:10.1115/1.1795241 History: Received December 05, 2003; Revised March 18, 2004; Online November 16, 2004
Copyright © 2004 by ASME
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Figures

Grahic Jump Location
Schematic of the multilayer structure. The “unit cell” consists of two nonabsorbing materials which have refractive indices of 4 and 2, respectively. The thickness of individual layer is d.
Grahic Jump Location
The total hemispherical transmittance of three periodic structures as a function of the number of total layers. The individual layer thicknesses of the structures are 5 nm, 10 nm and 50 nm, respectively, which are much less than the coherence length. The thickness dependence of the transmittance is due to interference effects.
Grahic Jump Location
The thickness dependence of the total hemispherical transmittance for up to three layers. The refractive index of each layer is given in the illustration. In the thick film region, the transmittance values of all three structures approach constants, which are close to the values predicted by ray tracing method.
Grahic Jump Location
The total hemispherical transmittance of three periodic structures as a function of the number of total layers. The individual layer thicknesses of the structures are 3 μm, 8 μm and 30 μm, respectively, which are larger than the coherence length. The transmittances calculated using the wave optics method for different thicknesses overlap and approach a nonzero value, while that calculated using the ray tracing method asymptotically approaches zero.
Grahic Jump Location
(a) The spectral directional transmittance of a 100-layer periodic structure for normal incident waves. The thickness of individual layers is 8 μm. Stop band and pass band are shown in the figure, (b) The spectral hemispherical transmittance for the same structure.
Grahic Jump Location
(a) The total hemispherical transmittance as a function of the number of layers, where σ is the order of randomness and lc is the localization length. The base thickness of individual layers is larger than the coherence length. (b) The averaged and non-averaged transmittance. (c) The y axis is Log(T). In the presence of high order of randomness (σ=4 lc) and large number of layers, the transmittance decays exponentially.
Grahic Jump Location
The spectral hemispherical transmittances of different random systems, where σ is the order of randomness and lc is the localization length. High frequency (short wavelength) components are localized relatively more easily.

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