Intensity Temporal Autocorrelation (G2)

Definition: Intensity Temporal Autocorrelation ( $G_2$ ) or its normalized form, “Normalized Intensity Temporal Autocorrelation ( $g_2$ )”, is the most commonly measured quantity in Diffuse Correlation Spectroscopy (DCS) measurements. Normalized Electric Field Autocorrelation function is often derived from $g_2$ using the so-called “Siegert Relation” which is used to fit DCS data. In Siegert relation, the relationship between $g_2(\tau)$ and $g_1(\tau)$ is; $g_2(\tau) = 1 + \beta |g_1 (\tau) |^2$ . In this equation, $\beta$ is an experimental factor which is equal to 1 for an ideal experimental design.Its formal definition is $G_2 ({\bf{r},\tau,t) = <I(\bf{r}, t) I(\bf{r}, t + \tau)>$ where $\bf{r}$ is the source-detector separation/position, $\tau$ is the delay time in the autocorrelation, $t$ is time and $<...>$ indicate ensemble averages.

Category: Physics

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

Abbreviation or symbol:

$G_2$