Fluorescence lifetime imaging with cost-efficient time-correlated photon counter

Fluorescence lifetime measurement is a versatile tool for studying the dynamics of biological, chemical, and quantum systems. However, commercially available time-correlated single-photon counting systems are typically very costly and are limited in terms of flexibility. Here, we present the use of a cost-efficient time-to-digital converter chip as a time-correlated single-photon counting module and the integration of the module into a confocal microscopy system to perform fluorescence lifetime imaging microscopy (FLIM). The system can withstand a sustained count rate of 10 000 counts per second with a timing uncertainty less than 170 ps full width at half maximum. FLIM measurement is obtained by scanning the confocal microscope over the sample and acquiring photon arrival times at each position, where the fluorescence lifetime is then computed using the fit-free center of mass method. The combined system is verified by imaging of fluorescence microbeads with known lifetimes, and we demonstrate the use of the system for imaging single-photon emitters with the nitrogen-vacancy defects in diamond. This timing module and calculation method can be used as a standalone upgrade kit for an existing microscope to enable FLIM measurement in biological studies and medical diagnosis applications.