  So far the current ground-based Imaging Atmospheric Cherenkov Telescopes
(IACTs) have energy thresholds in the best case in the range of ~30 to 50 GeV
(H.E.S.S. II and MAGIC telescopes). Lowest energy gamma-ray showers produce low
light intensity images and cannot be efficiently separated from dominating
images from hadronic background. A cost effective way of improving the
telescope performance at lower energies is to use novel photosensors with
superior photon detection efficiency (PDE). Currently the best commercially
available superbialkali photomultipliers (PMTs) have a PDE of about 30-33%,
whereas the silicon photomultipliers (SiPMs, also known as MPPC, GAPD) from
some manufacturers show a photon detection efficiency of about 40-45%. Using
these devices can lower the energy threshold of the instrument and may improve
the background rejection due to intrinsic properties of SiPMs such as a superb
single photoelectron resolution. Compared to PMTs, SiPMs are more compact, fast
in response, operate at low voltage, and are insensitive to magnetic fields.
SiPMs can be operated at high background illumination, which would allow to
operate the IACT also during partial moonlight, dusk and dawn, hence increasing
the instrument duty cycle. We are testing the SiPMs for Cherenkov telescopes
such as MAGIC and CTA. Here we present an overview of our setup and first
measurements, which we perform in two independent laboratories, in Munich,
Germany and in Barcelona, Spain.
