Parameterization of the angular response of 2.54-cm photomultiplier tubes

Photomultiplier tubes are used widely in nuclear and particle physics for the detection of light. There is, however, a certain amount of debate in the literature as to how to parameterize the photocathode and how to describe the angular dependence of the photomultiplier response function. I outline a method for parameterizing a photocathode in terms of its thickness tau and complex refractive index ñ. These parameters are measured for a pair of 2.54-cm photomultiplier tubes and used to predict the response as a function of angle. Comparison of this function with experimental data shows a clear correlation.