Spatial coherence of the thermal electromagnetic field in the vicinity of a dielectric slab

Wah Tung Lau, Jung-Tsung Shen, Georgios Veronis, and Shanhui Fan
Phys. Rev. E 76, 016601 – Published 10 July 2007

Abstract

We present the analytic calculation of the cross-spectral density tensor of a thermally radiative planar dielectric slab in extreme near-field, intermediate near-field, and far-field zones. We show that the spatial coherence of the thermal field exhibits distinct features in these zones. At a given wavelength λ, the coherence length is many orders of magnitude smaller than λ in the extreme near-field zone, and is roughly λ2 in the far-field zone. In the intermediate near-field zone, the coherence length can be much longer than λ2 if the loss is small. The physical origin of the short-ranged spatial coherence in the extreme near-field zone is the spatially fluctuating surface charges at the air-dielectric interface. We also demonstrate that in the intermediate near-field zone, the long-ranged spatial coherence is induced by the waveguide modes of the dielectric slab. When the loss is small, the long-ranged coherence falls off approximately as 1x, in contrast to 1x for a blackbody radiator, where x refers to displacement parallel to the slab surface.

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  • Received 19 October 2006

DOI:https://doi.org/10.1103/PhysRevE.76.016601

©2007 American Physical Society

Authors & Affiliations

Wah Tung Lau1,2, Jung-Tsung Shen2, Georgios Veronis2, and Shanhui Fan1,2,*

  • 1Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA
  • 2Ginzton Laboratory, Stanford University, Stanford, California 94305, USA

  • *shanhui@stanford.edu

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Vol. 76, Iss. 1 — July 2007

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