Breakthrough light harvesting in time-domain diffuse optics with 100 mm2 silicon photomultiplier

Time-Domain Diffuse Optics (TDDO) technologies are rapidly evolving towards compact and cheap devices, thus progressively reducing the gap with continuous-wave equivalent technologies while providing the additional advantages of higher information content and better depth penetration and selectivity. One of the key limitations for TDDO is the active area of microelectronic time-resolved single-photon detectors as it is not possible to efficiently focus Lambertian light exiting from highly scattering samples into small areas. Therefore, signal-to-noise ratio bottlenecks can be surpassed only by targeting a breakthrough in this direction. In this work we present the validation in laboratory settings of the largest detector (100 mm2 active area with 92% cells fill-factor) ever reported to our knowledge in TDDO applications. To objectively validate this device, we made use of established performance assessment protocols in the field of diffuse optics, which also define standard conditions enabling realistic benchmarking of novel devices. The detector demonstrated the largest light harvesting capability ever reported, capability to measure homogeneous optical properties in line with state-of-the-art devices, and superior depth penetration inside heterogeneous media (in reflectance geometry) with respect to all the previously reported technologies (i.e., >4 cm). The active area breakthrough permits to envisage the first TDDO measurements on different fruits in transmittance geometry, thus increasing the penetration depth with respect to the traditional reflectance approach and making it easier for a future evolution towards real time quality check of fruits on the conveyor belt.