All previous applications of diffusing-wave spectroscopy to aqueous foams have relied on the assumption that the electric field of the detected light is a Gaussian random variable and hence that the Siegert relation applies. We test this crucial assumption by simultaneous measurement of both second- and third-order temporal intensity correlations. We find that the electric field is Gaussian for typical experimental geometries equivalent to illumination and detection with a plane wave, both for backscattering and transmission through an optically thick slab. However, we find that the Gaussian character breaks down for point-in–point-out backscattering geometries in which the illumination spot size is not sufficiently large in comparison with the size of the intermittent rearrangement events.
© 2006 Optical Society of America
Photon Correlation and Scattering
Original Manuscript: November 4, 2005
Manuscript Accepted: November 25, 2005
Vol. 1, Iss. 5 Virtual Journal for Biomedical Optics
Alex S. Gittings and Douglas J. Durian, "Gaussian and non-Gaussian speckle fluctuations in the diffusing-wave spectroscopy signal of a coarsening foam," Appl. Opt. 45, 2199-2204 (2006)