The measurement of the time-dependent fluctuations in the scattered intensity of coherent monochromatic light. These fluctuations arise because the particles are small enough to undergo random thermal (Brownian, q.v.) Motion, and the distance between them is therefore constantly varying. The measurement yields the diffusion coefficient of the particles from which, via the Stokes-Einstein equations, and knowing the viscosity of the medium, the hydrodynamic radius (or diameter) can be calculated.

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A technique for estimating nanoparticle sizes by measuring fluctuations in light scattered by the sample. Also known as photon correlation spectroscopy or quasi-elastic light scattering.

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Method of determining the hydrodynamic diameter by measuring the diffusion speed of particles or molecules undergoing Brownian motion, using a coherent laser beam illuminating the material dispersed at a suitable concentration in a liquid. The decay of the autocorrelation function of the measured intensity of the scattered light is interpreted as an average particle size and polydispersity index can be obtained using the cumulants method, and information about size distribution

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