Nonimaging light concentrators for photomultiplier tubes with nonuniform response of the photocathode

The relative efficiency of the photocathode of a photomultiplier tube may not be uniform over its entire diameter. A special kind of concentrator should be designed in order to send more light onto the area of the photocathode that has a higher efficiency. A design method for obtaining such a concentrator is described and the two new concentrators obtained are analyzed by ray-tracing. The capacity of the classic compound parabolic concentrator to direct more light on the areas of higher efficiency is also analyzed and the results are compared to those of the two new concentrators proposed. The total efficiency of light conversion is evaluated for the new designs proposed and the classic CPC in the case of a Hamamatsu R-7056 photomultiplier tube to be used by the VERITAS project [1].