Use of lenses to increase the RICH photodetector coverage

A novel lens arrangement is described, that can be placed in front of multianode photomultipliers to increase their geometrical coverage to almost 100the photon incident angle out to 400 mrad, allowing its use with aerogel as well as gas radiators. The array of lenses can also serve to separate the photodetectors from the radiator gas, and as only a single gas/lens interface is introduced there is no penalty from reflection loss.1