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).