The light-trap: a novel concept for a large SiPM-based pixel

Many applications in high energy astrophysics, particle physics or medical imaging demand covering a large detection area with fast photosensors sensible to near-UV light. The use of Silicon photomultipliers (SIPMs) for such applications is restricted due to their sensitivity to unwanted wavelengths and mainly due to their limited physical area, increasing the cost and readout complexity of a camera. We propose to solve these drawbacks by building a Light-Trap, a low-cost pixel consisting on a SiPM attached to a PMMA disk doped with a wavelength shifter (WLS). Light in the near-UV band absorbed by the WLS is optically trapped inside the disk volume until it reaches the SiPM. The pixel collects photons over a much larger area than standard SiPMs, while being sensitive only in a desired wavelength range, which can be selected to match the application requirements. We introduce the Light-Trap principles and discuss results from laboratory measurements and Monte Carlo simulations.