Imaging optical adapters for multi-anode photo multipliers detectors

In several experiments of Nuclear and Neutrino Physics and Cosmic-rays detection, Multi-Anode Photo-Multipliers (MAPMTs) detectors from Hamamatsu corp. are used. Aim of this work is to describe the ancillary optical system, projected to improve the photons collection efficiency of PMT detectors focusing all photons inside the sensitive area. This system optimized with ray-tracing simulations allows to maintain imaging and filtering capability, improving the signal-to-noise ratio by limiting the wave band to the region of interest. The filter glass employing and the multi-layer coating optimization allows to avoid background photons from nearby spectral regions and to minimize the wavelength shifting when the incident angle increases. The transmissivity spectrum has been realized with an high transparency in wavelength range of interest and with a sharp cut-off outside. First prototypes have been realized.