Fast time-correlated single photon counting system to overcome pile-up limitation with single photon avalanche diodes

Time-Correlated Single Photon Counting (TCSPC) is generally recognized as a powerful tool for Fluorescence Lifetime Imaging (FLIM), thanks to its inherently high sensitivity and timing precision. Nevertheless, one of the major drawbacks of the technique is represented by the so-called pile-up distortion, that typically limits the acquisition rate to few percent of the laser stimulation rate. In recent years, an innovative methodology has been proposed to overcome this restriction: by matching the detector dead time to the laser period an average acquisition rate of 40 Mcps is achieved, along with negligible distortion. In this work, we present the first single-channel system that implements the new measurement technique. To this aim, two modules have been specifically developed to accommodate a custom-technology Single-Photon Avalanche Diode (SPAD) and its dedicated acquisition chain. On one hand, a compact Detection Module hosts both a fully-integrated Active Quenching Circuit (AQC) to provide a finely-tunable dead time and a differential Pick-Up Circuit (PUC) to extract a picosecond-precision timing signal. On the other hand, a Time Conversion module is intended to acquire the fast timing signal thanks to a mixed-architecture Fast Time to Amplitude Converter (F-TAC). The experimental characterization proved that the modules feature excellent performance both in terms of timing precision (55 ps FWHM) and Differential Nonlinearity (4 % LSB peak to peak) and we're now ready to compare the new technique with the classic pile-up limited approach in a real application on field.

Automated summary

TCSPC is a powerful tool for FLIM due to its high sensitivity and timing precision, but is limited by pile-up distortion. An innovative methodology has been proposed to overcome this limitation by matching detector dead time to laser period, achieving high acquisition rates. Experimental characterization of the new system showed excellent performance in timing precision and now the new technique is ready for real-world comparison with classic approaches.