Time-Correlated Single-Photon Counting Measurements: A New Approach for High-Speed

When high timing resolution and extremely low sensitivity are needed for the analysis of optical signals, Time-Correlated Single-Photon Counting (TCSPC) is one of the preferred techniques [1]. Fluorescence Lifetime Imaging (FLIM) and single-molecule analysis are examples of applications in which these features, together with non-invasivity, are fundamental. Unfortunately, long acquisition time characterises this technique, preventing its use in many other advanced applications, where real time imaging is needed. To make the situation even worse, there is an ultimate limit on the excitation rate, which is imposed by the so called classic pile-up. Indeed, in a TCSPC measurement, it is the major source of distortion, since it allows the system to record only first impinging photons, losing the subsequent; for this reason the count rate of each acquisition channel is kept between 1%-5% of the laser repetition rate.