SiPM for atmospheric Cherenkov telescopes

In the recent twenty five years the technique of imaging atmospheric Cherenkov telescopes for ground-based very high energy gamma-ray astrophysics has emerged and rapidly established itself as a new powerful discipline in science. The next generation large instrument, known under the name Cherenkov Telescope Array, will soon move from the prototyping into the construction phase. Its sensitivity will be an order of magnitude higher than that of the currently leading instruments VERITAS, H.E.S.S. and MAGIC. Currently, the standard light sensors for IACTs are the classical photo multipliers. Since very recently photo multipliers with a peak quantum efficiency of 40% are becoming available. In addition, also the photo electron collection efficiency on the first dynode has been increased to similar to 95-98%, providing a photon detection efficiency that is almost as high as the quantum efficiency. SiPMs, also known as MPPC, GAPD, Micro-channel APD, are novel semiconductor light sensors that are rapidly maturing. Compared to photo multiplier tubes the currently best SiPM have comparable photon detection efficiency, better amplitude and time resolution, but much worse noise. Their parameters are steadily improving and sometime in the future they may become almost ideal light sensors, substituting classical photo multiplier tubes in many applications. Also in astrophysics they can find wide applications. In this report we will dwell on the potential and advantages of using SiPM for Cherenkov telescopes.