A technique for the measurement of the time histogram of a @[email protected] of photons with respect to a periodic event, e.g. a flash from a repetitive nanosecond @[email protected] or a CW operated @[email protected] (@[email protected] locked @[email protected]). The essential part is a time-to-amplitude-converter (TAC) which transforms the arrival time between a start and a stop pulse into a voltage. Sometimes called single photon timing.