2012 BFY Abstract Detail Page
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||W18 - Simple Dynamic Light Scattering Apparatus
||A HeNe laser beam, incident on a sample of micron-sized spheres suspended in water, scatters into a random pattern of spots of varying size, shape, and intensity. The pattern results from the coherent superposition of the outgoing waves scattered from the spheres and because the spheres are in constant Brownian motion, the pattern changes in time. An avalanche photodiode detector is placed in the pattern to measure the random fluctuations in the light intensity. The autocorrelation function and the power spectrum of the photodiode signal are computed, averaged over time, and fit to predictions based on Brownian motion. The fitting model parameters are then used to determine the diameter of the spheres.
The apparatus will be available for use and complete construction and analysis details will be provided. The geometry of the source, scattering cell and detector will be discussed in relation to the scattering angle dependence of the intensity fluctuations. The circuit for the avalanche photodiode will be provided and the computer hardware and software for collecting and analyzing the signal will be demonstrated. The results for two sphere sizes as a function of scattering angle will be presented.
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University of Florida
Department of Physics
Phone: (352) 392-1690