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Twiss (HBT) photon correlator. 

Figure 2 (a) shows a wide-field CCD camera image of DBT molecules in an AC film. Individual molecules can be clearly distinguished. By switching to confocal excitation, we selected individual molecules for further investigations. The inset in Fig, 2 (b) displays the fluorescence spectrum of a DBT molecule. It has its maximum at 790 nm and a width of about 50 nm. However, because the detection efficiency of the spectrometer drops between 850 nm and 900 nm by more than a factor of two, the spectrum is slightly distorted in this wavelength range. To gain further information on the molecule’s properties, we directed the photons generated by pulsed excitation on an APD and applied a time correlated single- 

