Fast Gating of Single-Photon Avalanche Diodes for Photon Migration Measurements

Abstract

Near-Infrared (NIR) picosecond pulsed light shined in biological tissues offers the opportunity for non-invasive imaging. We aimed at developing a winning photodetector electronics pairing for a broad field of multiple-wavelengths faint-signal optical investigations, like functional brain imaging. We present an electronic instrumentation based on silicon Single-Photon Avalanche Diode (SPAD) and fast-gating front-end electronics, in a time-correlated single-photon counting set-up. The high detection efficiency allows the acquisition of very faint optical signals on a wide spectral range. Furthermore, the fast gating circuitry enables the detector very quickly (400 ps), thus allowing the rejection of very intense light scattered from more superficial layers of the head, preceding useful faint signal scattered from the brain. We attain photon-counting dynamic ranges up to 107 with photon-timing resolutions of 95 ps, thus allowing the detection of photons delayed up to 6 ns from the laser stimulus.