Complete and Compact 32-Channel System for Time-Correlated Single-Photon Counting Measurements

Single-photon detectors play a key role in many research fields such as biology, chemistry, medicine, and space technology, and in recent years, single-photon avalanche diodes (SPADs) have become a valid alternative to photo multiplier tubes (PMTs). Moreover, scientific research has recently focused on single-photon detector arrays, pushed by a growing demand for multichannel systems. In this scenario, we developed a compact 32-channel system for time-resolved single-photon counting applications. The system is divided into two independent modules: a photon detection head including a 32 $times$ 1 SPAD array built in custom technology, featuring high time resolution, high photon detection efficiency (44% at 550 nm), and low dark count rate (mean value $ 400 cps at $-10 ^{circ}hbox{C}$) at 6-V excess bias voltage and a 32-channel acquisition system able to perform time-correlated single-photon counting (TCSPC) measurements. The TCSPC module includes eight four-channel time-to-amplitude converter (TAC) arrays, built-in 0.35-$mu$m Si-Ge BiCMOS technology, characterized by low differential non-linearity (rms value lower than 0.15% of the time bin width) and variable full-scale range. The system response function of this TCSPC instrumentation achieves a mean time resolution of 63 $hbox{ps}_{rm FWHM}$, considering a mean count rate of 1 Mcps.