Late Output Pulses from Fast Photomultipliers

Fast photomultipliers operating in the single-photoelectron limit exhibit a bimodal time distribution of output pulses; typically, 0.01 of output pulses occur several nanoseconds later than the most probable time. Correlation techniques can be used to characterize photomultiplier time response, and results are given for some commonly used tubes. Late pulse probability is a function of some tube parameters, but even when it is minimized, the effects of late pulses are significant in uses of single-photon counting such as the study of macromolecule fluorescence decay.