Modular Wavelength-Shifting Photon Detector with SiPM Readout for Large-Area Applications

Wavelength shifters (WLS) offer a scalable and affordable approach to large-area photon detection. They absorb photons and re-emit them at longer wavelengths, enabling efficient light trapping by total internal reflection. We present a compact detector module based on WLS tiles coupled to silicon photomultipliers (SiPMs). The design exploits the geometry of elongated photodetectors placed along the tile edges to maximize photon collection without requiring large sensor surfaces. Particular attention was given to matching the spectral response of the WLS and the SiPMs to the Cherenkov emission peak. Laboratory tests with a pulsed UV laser provide preliminary measurements of the photon-detection efficiency and pulse shape. For the single-shift configuration, a preliminary photon-detection efficiency of about 20% was measured. First pulse-shape studies indicate a signal width of approximately 5 ns FWHM, reflecting the impact of wavelength shifting and optical reflections on signal broadening. While the absolute efficiency is lower than conventional solutions, the modularity and scalability of the system make it a promising candidate for large-area photon detection. Further studies will address detailed timing resolution and array-level performance.