Fluorescence correlation spectroscopy (FCS) is a common technique used by physicists, chemists, and biologists to experimentally characterize the dynamics of fluorescent species (e.g. Single fluorescent dye molecules in nanostructured materials, autofluorescent proteins in living cells, etc.). Although the name indicates a specific link to fluorescence, the method is used today also exploring other forms of luminescence (like reflections, luminescence from gold-beads or quantum dots or phosphorescent species). The "spectroscopy" in the name is not readily found as in common usage a spectrum is generally understood to be a frequency spectrum. The autocorrelation is a genuine form of spectrum, however: It is the time-spectrum generated from the power spectrum (via inverse fourier transform).

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Method to determine the diffusion coefficients of molecules by measuring the decay kinetics of fluorescence excited by polarized light NOTE Also known as fluorescence anisotropy decay spectroscopy.

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