The use of silicon photomultipliers for very high energy gamma ray astronomy: the optical issues

Due to its sensitivity and speed, the detector still widely used in Cerenkov astrophysics experiments remains the Photo-Multiplier Tube (PMT). However, there are some disadvantages to the PMT technology: the rather poor quantum efficiency, the use of high voltages, the high cost when used in large number in a matrix arrangement and a subsequent large weight. Hence, we have investigated the possibility to design future Cerenkov telescope cameras based on solid state technology, specifically Geiger Avalanche PhotoDiodes (G-APD’s). This paper describes our extensive simulations to design the optical setup to be employed with G-APD’s. We also discuss the reflector configurations, pixel layouts, light concentrators, microlens arrays and spectral efficiencies to optimize light collection. The electronic aspects of our work were presented in a recent companion paper (Pellion et al., Exp. Astron. 27(3):187, 2010 ).