Technique for the measurement of photomultiplier transit time variation

An instrumental technique is described for measuring the variations of transit time of signals through a photodetector as a function of the position of the light beam on the photosurface. Precision of 3 psec may be obtained with simple, commercial components; a coherent light source is not required. Data are given for two types of photomultipliers, showing the fine structure of the transit time behavior and the effects of beam diameter. A contour map of equal transit time regions is shown for one of the tubes tested. The results are of interest in certain optical systems used in measuring distance and speed of light determinations.