see also:

Time Correlated Single Photon Counting, time domain FLIM, tdFLIM

In Time-correlated single-photon counting (TCSPC) fluorescence decays are measured over the time axis. The method is an essential part of fluorescence lifetime imaging microscopy (FLIM). Time-Correlated Single Photon Counting is considered a particularly gentle measurement technique because the light pulses required for sample excitation have low pulse energy. This is possible because only a single photon is processed at a time. TCSPC is based on the detection of these individual photons and the measurement of their arrival times in relation to a reference signal, which is usually the time of emission of the laser pulse that was used to excite the sample. This laser pulse occurs with a high repetition rate so that a sufficiently high number of individual photons can be determined for the resulting measurement of the fluorescence lifetime.