Single photon timing system for picosecond fluorescence lifetime measurementsa)

A single-photon timing system is described which is capable of extracting fluorescence lifetimes as short as 25 ps. The system is an improved version of an earlier apparatus. The new system uses a synchronously pumped, mode-locked dye laser with 10-ps pulses operating at 82-MHz repetition rate. A fast photodetector and a leading-edge discriminator were developed to use with this light source. Also, a special rate reduction circuit was built to eliminate large oscillations in fluorescence decay spectra due to the excessive stop rates that overload commercial time-to-amplitude converters.