32 Mcps time-correlated single photon counting with a single SPAD avoiding pile-up

Time-Correlated Single Photon Counting (TCSPC) is a time-resolved and ultrasensitive technique, that provides the analysis of optical pulses to a wide range of different applications both in the biological and chemical domain. Nevertheless, an ultimate constraint to this technique has been historically posed by pile-up distortion, that typically restricts the maximum acquisition speed to few percent of the laser excitation rate. To surpass this fundamental limitation, a novel theoretical solution has been reported in a previous paper: with a perfect matching between detector dead time and laser period, it is possible to achieve a high-speed measurement, still maintaining negligible distortion. In this work, we present the design, characterization and experimental validation of a single-channel TCSPC system that implements the proposed idea. The essential core of the system consists in a compact Detection Head featuring a finely tunable dead time, thanks to a fully-integrated front-end electronics coupled to a custom technology Single-Photon Avalanche Diode (SPAD). This module is providing a picosecond precision timing signal, that is then acquired and digitized by means of a Fast Time to Amplitude Converter (F-TAC) architecture, followed by a high-end Field Programmable Gate Array (FPGA). In order to validate the proposed technique, we carried out on-field fluorescence lifetime measurements employing the newly developed system. The experimental results show good accordance with the previous theoretical framework. It is therefore possible to achieve high acquisition speed (32 Mcps) with an almost null lifetime distortion, thus paving the way to new advanced TCSPC applications.