Muon ring images with an atmospheric Čerenkov telescope
High energy muons generated by air showers can be detected with atmospheric Cerenkov imaging telescopes via their ring signature. The distribution of Cerenkov light along the ring is a function only of the muon's distance of impact from the telescope: this property makes possible the calibration of the photon collection efficiency of imaging telescopes. We evaluate the acceptance of an imaging Cerenkov telescope to muons and discuss its application to the study of cosmic rays. We point out that muons may set a gamma-ray flux sensitivity limit for ground-based gamma-ray telescopes.
Using a pump-probe Michelson experiment, we test the theory of thermo-optic (TO) effects in dielectric mirror coatings. We observe partial cancellation between coating expansion and TO effects. We also measure relevant thin film material parameters.