Autocorrelation Function
The (temporal) autocorrelation function is the correlation of a time series with itself shifted by time, as a function of :
where is the deviation from the mean intensity. The normalization (denominator) here is the most commonly used for FCS, because then the correlation at, G(0), is related to the average number of particles in the measurement volume.
As an example, raw FCS data and its autocorrelation for freely diffusing Rhodamine 6G are shown in the figure to the right. The plot on top shows the fluorescent intensity versus time. The intensity fluctuates as Rhodamine 6G moves in and out of the focal volume. In the bottom plot is the autocorrelation on the same data. Information about the diffusion rate and concentration can be obtained using one of the models described below.
Read more about this topic: Fluorescence Correlation Spectroscopy
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