Spatial coherence of sunlight: First direct measurement

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

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Scopus citations


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.

Original languageEnglish
Title of host publicationNonimaging Optics
Subtitle of host publicationEfficient Design for Illumination and Solar Concentration IX
StatePublished - 1 Dec 2012
EventNonimaging Optics: Efficient Design for Illumination and Solar Concentration IX - San Diego, CA, United States
Duration: 12 Aug 201214 Aug 2012

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


ConferenceNonimaging Optics: Efficient Design for Illumination and Solar Concentration IX
Country/TerritoryUnited States
CitySan Diego, CA

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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