Spatial coherence of sunlight: first direct measurement

Heylal Mashaal; Alex Goldstein; Daniel Feuermann; Jeffrey M. Gordon

doi:10.1117/12.928449

11 October 2012 Spatial coherence of sunlight: first direct measurement

Heylal Mashaal, Alex Goldstein, Daniel Feuermann, Jeffrey M. Gordon

Proceedings Volume 8485, Nonimaging Optics: Efficient Design for Illumination and Solar Concentration IX; 84850A (2012) https://doi.org/10.1117/12.928449
Event: SPIE Optical Engineering + Applications, 2012, San Diego, California, United States

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.

Citation Download Citation

Heylal Mashaal, Alex Goldstein, Daniel Feuermann, and Jeffrey M. Gordon "Spatial coherence of sunlight: first direct measurement", Proc. SPIE 8485, Nonimaging Optics: Efficient Design for Illumination and Solar Concentration IX, 84850A (11 October 2012); https://doi.org/10.1117/12.928449

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