Abstract
The Brownian/diffusive motion of micrometer-sized, suspended particles has been observed by using heterodyne light scattering with frequency-modulation (FM) detection and signal processing. The FM output is linear in the coherent velocity of the particles, with the random diffusive velocity component giving rise to background noise in the FM output. Experimental measurements of polystyrene latex spheres in water corroborate the predicted result for the signal-to-noise ratio. The noise component of the FM output was found to be independent of the particle number and, within the instrumental bandwidth, to be flat. Good quantitative agreement between the predicted and measured noise backgrounds was obtained for particle diameters from 0.5 to 50 μm.
© 1987 Optical Society of America
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