Vacuum silicon photo multiplier tube (VSiPMT): Towards a new generation of photon detectors

Photomultiplier tubes (PMT) technology has been improved continuously in the last years: the quantum efficiency of the photocathode has now reached a level of 40%, close to the theoretical maximum; single photon sensitivity and time resolution have been improved by a careful design of electrostatic focusing on the 1st dynode; with new coatings the secondary electron yield of dynodes has greatly improved, reducing the required number of dynodes and their size. Nevertheless standard photomultiplier tubes suffer the following drawbacks: fluctuations in the first dynode gain make single photon counting difficult; linearity is strongly related to the gain and decreases as the latter increases; transit time spreads over large fluctuations; mechanical structure is complex, voluminous, rather massive and expensive; they are sensitive to magnetic fields. The Vacuum Silicon PhotoMultiplier Tube (VSiPMT) is an innovative photodetector based on the combination of SiPM (Silicon PhotoMultiplier) and PMT technologies proposed to overcame the described PMTs limits. In this paper, we give a description of the device and experimental results on its prototypes, as our studies and our purposes towards an optimized device.