We describe a multispeckle dynamic light scattering technique capable of resolving the motion of scattering sites in cases that this motion changes systematically with time. The method is based on the visibility of the speckle pattern formed by the scattered light as detected by a single exposure of a digital camera. Whereas previous multispeckle methods rely on correlations between images, here the connection with scattering site dynamics is made more simply in terms of the variance of intensity among the pixels of the camera for the specified exposure duration. The essence is that the speckle pattern is more visible, i.e., the variance of detected intensity levels is greater, when the dynamics of the scattering site motion is slow compared to the exposure time of the camera. The theory for analyzing the moments of the spatial intensity distribution in terms of the electric-field autocorrelation is presented. It is tested for two well-understood samples, a colloidal suspension of Brownian particles and a coarsening foam, where the dynamics can be treated as stationary and hence can be benchmarked by traditional methods. However, our speckle-visibility method is particularly appropriate for samples in which the dynamics vary with time, either slowly or rapidly, limited only by the exposure time fidelity of the camera. Potential applications range from soft-glassy materials, to granular avalanches, to flowmetry of living tissue.
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September 2005
Research Article|
September 07 2005
Speckle-visibility spectroscopy: A tool to study time-varying dynamics
R. Bandyopadhyay;
R. Bandyopadhyay
a)
Department of Physics and Astronomy,
University of California
, Los Angeles, California 90095
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A. S. Gittings;
A. S. Gittings
Department of Physics and Astronomy,
University of California
, Los Angeles, California 90095
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S. S. Suh;
S. S. Suh
Department of Physics and Astronomy,
University of California
, Los Angeles, California 90095
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P. K. Dixon;
P. K. Dixon
b)
Department of Physics and Astronomy,
University of California
, Los Angeles, California 90095
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D. J. Durian
D. J. Durian
c)
Department of Physics and Astronomy,
University of California
, Los Angeles, California 90095
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a)
Permanent address: Liquid Crystals Laboratory, Raman Research Institute, Bangalore 560080, India; electronic mail: ranjini@rri.res.in
b)
Permanent address: Department of Physics and Astronomy, California State University, San Bernardino, CA 92407; electronic mail: pdixon@csusb.edu
c)
Permanent address: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104; electronic mail: djdurian@physics.upenn.edu
Rev. Sci. Instrum. 76, 093110 (2005)
Article history
Received:
June 06 2005
Accepted:
July 18 2005
Citation
R. Bandyopadhyay, A. S. Gittings, S. S. Suh, P. K. Dixon, D. J. Durian; Speckle-visibility spectroscopy: A tool to study time-varying dynamics. Rev. Sci. Instrum. 1 September 2005; 76 (9): 093110. https://doi.org/10.1063/1.2037987
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