Speed-optimization strategies for time-correlated single photon counting experiments

Time-correlated single photon counting (TCSPC) is recognized as a gold-standard technique in many fields, including life science and remote sensing applications. In particular, it is the enabling technology to record extremely fast luminous signals with accuracy down to a few picoseconds. However, setup limits like the presence of pile-up and dead-time-related phenomena impose a strong limitation to the speed of TCSPC experiments. In particular, the average number of recorded events is typically limited below 0.05 photons per excitation period, and also in those cases where the sample can emit a significantly higher photon rate. Many efforts have been done in the past few years to maximize speed, including the design of fast detectors and associated electronics, with nanosecond and sub-nanosecond dead time and multi-hit capabilities. Moreover, new advanced techniques have been proposed to get rid of distortion phenomena, thus enabling unprecedented speed. The goal of this paper is to provide a deep understanding of the ultimate limits to measurement speed, considering the best solutions presented so far. A general step-by-step methodology is proposed to calculate maximum speed in different conditions and to select the best suited technology to push speed to the edge depending on specific operation cases.