Noise in the Measurement of Light with Photomultipliers

In order to be able to compare light intensity measurements derived from the anode current of a photomultiplier with measurements derived from photoelectron pulse counting, a systematic investigation of the properties of some photomultiplier tubes has been made. This has led to a correlation of the properties of a photomultiplier based on an over-all quantum efficiency etaF, the gain G, a photoelectron noise factor S, and an effective dark rate D. In terms of these quantities the signal-to-noise ratio of an experimental measurement can be calculated, given the light flux and measurement technique. It is shown that the noise power spectral density is constant for a photomultiplier, down to about 10(-2) Hz, and that pulse counting and current measurement will give similar signal-to-noise ratios under most experimental conditions.