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Proceedings Paper

Spatial coherence of sunlight: first direct measurement
Author(s): Heylal Mashaal; Alex Goldstein; Daniel Feuermann; Jeffrey M. Gordon
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Paper Abstract

We report the first direct measurement of the spatial coherence of solar beam radiation. Although often perceived as incoherent, direct sunlight exhibits spatial coherence at a sufficiently small scale. These dimensions were recently derived theoretically to be around two orders of magnitude greater than the wavelength. The partial coherence of sunlight raises tantalizing prospects for a new paradigm for solar power conversion via the antenna effect exploited so successfully in radio-frequency and microwave technologies (albeit at frequencies of order 1 PHz for solar). After reviewing the equal-time mutual coherence function of sunlight, we explain the particular suitability of a lateral cyclicshearing interferometer wherein the solar beam is split into two parts that are subsequently recombined with a relative lateral displacement. The method is relatively uncomplicated, inexpensive and obviates the problem of component dispersion (potentially problematic for a light source as broadband as sunlight). The experimental results are in good agreement with the recent theoretical predictions.

Paper Details

Date Published: 11 October 2012
PDF: 5 pages
Proc. SPIE 8485, Nonimaging Optics: Efficient Design for Illumination and Solar Concentration IX, 84850A (11 October 2012); doi: 10.1117/12.928449
Show Author Affiliations
Heylal Mashaal, Ben-Gurion Univ. of the Negev (Israel)
Alex Goldstein, Ben-Gurion Univ. of the Negev (Israel)
Daniel Feuermann, Ben-Gurion Univ. of the Negev (Israel)
Jeffrey M. Gordon, Ben-Gurion Univ. of the Negev (Israel)

Published in SPIE Proceedings Vol. 8485:
Nonimaging Optics: Efficient Design for Illumination and Solar Concentration IX
Roland Winston; Jeffrey M. Gordon, Editor(s)

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