Effects and correctability of pile-up distortion using established figures of merit in time-domain diffuse optics at extreme photon rates.

Time-domain diffuse optics (TD-DO) allows one to probe diffusive media with recognized advantages over other working domains but suffers from a poor signal-to-noise ratio (SNR) resulting from the need to build-up the histogram of single-photon arrival times with maximum count rates (CR) of few percent of the laser pulse rate to avoid the so-called "pile-up" distortion. Here we explore the feasibility of TD-DO under severe pile-up conditions with a systematic in-silico/experimental study evaluating the effects and correctability of the distortion by means of shared figures of merit. In-silico, we demonstrate that pile-up correction allows one the retrieval of homogeneous optical properties with average error < 1% up to a CR > 99%, while the optimal CR needed to detect localized perturbation was found to be 83%. Experiments reported here confirm these findings despite exhibiting higher accuracy errors in the retrieval of homogeneous optical properties and higher noise in the detection of localized absorption perturbations, but in line with the state-of-the-art systems. This work validates a new working regime for TD-DO, demonstrating an increase of the SNR at constant acquisition time, but also potentially leading in the future to previously unrealizable measurements of dynamic phenomena or in spatial scanning applications.