**Definition:**Intensity Temporal Autocorrelation () or its normalized form, “Normalized Intensity Temporal Autocorrelation ()”, is the most commonly measured quantity in Diffuse Correlation Spectroscopy (DCS) measurements. Normalized Electric Field Autocorrelation function is often derived from using the so-called “Siegert Relation” which is used to fit DCS data. In Siegert relation, the relationship between and is; . In this equation, is an experimental factor which is equal to 1 for an ideal experimental design.Its formal definition is where is the source-detector separation/position, is the delay time in the autocorrelation, is time and indicate ensemble averages.

**Alternative definition:**

**Synonym:**Normalized Intensity Temporal Autocorrelation (g2)

**References:**

**Related terms:**Electric Field Temporal Autocorrelation Function, Diffuse Correlation Spectroscopy