Improving TCSPC data acquisition from CMOS SPAD arrays

We present a digital architecture for fast acquisition of time correlated single photon counting (TCSPC) timestamps from 32×32 CMOS SPAD array. Custom firmware was written to select 64 pixels out of 1024 available for fast transfer of TCSPC timestamps. Our 64 channel TCSPC is capable of acquiring up to 10 million TCSPC timestamps per second over a USB2 link. We describe the TCSPC camera (Megaframe), camera interface to the PC and the microscope setup. We characterize the Megaframe camera for fluorescence lifetime imaging (FLIM) including instrument response function, time resolution and variability of both across the array. We show a fluorescence lifetime image of a plant specimen (Convallaria majalis) from a custom-built multifocal multiphoton microscope. The image was acquired in 20 seconds (with average timestamp acquisition rate of 4.7 million counts per second).