Abstract
A light beam which has a constant amplitude and is incident on a photomultiplier cathode generates completely random current impulses. When the incident light intensity is fluctuating, the probability of generating current impulses is also fluctuating in time, and hence one will find current impulses obeying a compound Poisson process. The ratio of the variance to the average number of counts in successive time slots becomes larger than unity and dependent on the time slot width of the photon counting. The present paper gives a formula which reduces the shot noise level and derives the psd of the intensity fluctuations from the dependence of the variance-to-mean ratio on the time slot width. The limitation of this technique is discussed and the validity of the technique is demonstrated by computer simulation.