A Fluorescence Correlation Spectroscopy (FCS) measurement of a very diluted solution (1x10^-10 M) of freely diffusing Atto655 molecules in water was performed with a PDM module with an active area of 50 µm integrated in the MicroTime 200. A special modified LDH-P-635, running at cw operation at 640 nm was used for the excitation. The microscope was equipped with a 100x 1.3 NA objective and a 50 µm pinhole was used. The emission wavelength of Atto655 is in the range of 680 nm. All measurements were done in the TTTR mode of the TimeHarp 200 board. The measurement time for this example was 100 s.