In dynamic light scattering (DLS) a coherent light beam is sent through a sample, typically a solution of macromolecules, and the scattered light intensity I is detected as a function of scattering angle Θ and time t, I = I(Θ ,t). Brownian motion in the sample leads to intensity fluctuations, which depend on the speed of the moving molecules: fast motion will lead to rapid fluctuations.
