text: Laser light is sent to the sample and the outcoming transmitted or backscattered light is detected by an optoelectric sensor. The light intensity detected is the result of the interference of all the optical waves coming from the different light paths.
  The signal is analysed by calculating the intensity autocorrelation function called g. 
  For the case of non-interacting particles suspended in a (complex) fluid a direct relation between g-1  and the mean squared displacement of the particles > can be established. Let us note P(s) the probability density function (PDF) of the photon path length s. The relation can be written as follows:
  with  and  is the transport mean free path of scattered light.
  For simple cell geometries, it is thus possible to calculate the mean squared displacement of the particles > from the measured g-1 values analytically. For example, for the backscattering geometry, an infinitely thick cell, large laser spot illumination and detection of photons coming from the center of the spot, the relationship between g-1 and > is:
  , γ value is around 2.
  For less thick cells and in transmission, the relationship depends also on l* (the transport length).
  For quasi-transparent cells, an angle-independent variant method called cavity amplified scattering spectroscopy makes use of an integrating sphere to isotropically probe samples from all directions, elongating photon paths through the sample in the process, allowing for the study of low turbidity samples under the DWS formalism.