Large area SiPM and high throughput timing electronics: toward new generation time-domain instruments

We present here a novel time-domain diffuse optical detection chain consisting of a large area Silicon PhotoMultipliers (SiPM) coupled to a high count-rate timing electronics (TimeHarp 260 PICO) to achieve sustainable count-rates up to 10 Mcps without significant distortions to the distribution of time-of-flight (DTOF). Thanks to the large area of the detector (9 mm2) and the possibility to directly place it in contact with the sample (thus achieving a numerical aperture close to unity), the photon collection efficiency of the proposed detection chain is almost two orders of magnitude higher than traditional fiber-mounted PMT-based systems. This allows the detection also of the few late photons coming from deeper layers at short acquisition times, thus improving the robustness of the detection of localized inhomogeneities. We then demonstrate that, despite the high dark count rate of the detector, it is possible to reliably extract the optical properties of calibrated phantoms, with proper linearity and accuracy. We also explore the capability of the new detection chain for detecting brain activations. This work opens up the possibility of ultimate performance in terms of high signal and photon throughput, with compact, low cost, relatively simple front-end electronics detector coupled to innovative timing electronics, with exciting opportunities to expand it to tomographic applications.