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

Wah Tung Lau; Jung-Tsung Shen; Georgios Veronis; Shanhui Fan

doi:10.1117/12.761909

11 February 2008 Spatial coherence of the thermal electromagnetic field in the vicinity of a dielectric slab

Wah Tung Lau, Jung-Tsung Shen, Georgios Veronis, Shanhui Fan

Proceedings Volume 6901, Photonic Crystal Materials and Devices VII; 690109 (2008) https://doi.org/10.1117/12.761909
Event: Integrated Optoelectronic Devices 2008, 2008, San Jose, California, United States

Abstract

We analyze the spatial coherence of thermal field emitted from a lossy dielectric slab using fluctuation-dissipation theorem.¹ For a given wavelength λ, the coherence property varies drastically with the distance from the slab surface. The coherence length is roughly λ / 2 in the far-field zone, but in the extreme near-field zone, it is many orders of magnitude smaller than λ, due to spatially fluctuating surface charges at the air-dielectric interface. On the other hand, in the intermediate near-field zone, the coherence length can be much longer than λ / 2 if the loss is small, because of the presence of waveguide modes of the slab. Such long-ranged coherence falls off approximately as 1/√x , in contrast to 1/x for a blackbody radiator, where x refers to displacement parallel to the slab surface. Furthermore, at a point of fixed distance from the slab surface, the frequency spectrum of the local energy density exhibits distinct fluctuation pattern, which is shown to be closely related to the waveguide dispersion relation.

Citation Download Citation

Wah Tung Lau, Jung-Tsung Shen, Georgios Veronis, and Shanhui Fan "Spatial coherence of the thermal electromagnetic field in the vicinity of a dielectric slab", Proc. SPIE 6901, Photonic Crystal Materials and Devices VII, 690109 (11 February 2008); https://doi.org/10.1117/12.761909

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