A technique for the measurement of the time histogram of a @ST06775@ of photons with respect to a periodic event, e.g. a flash from a repetitive nanosecond @L03447@ or a CW operated @L03459@ (@M03958@ locked @L03459@). 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.