Time-resolved diffuse optical spectroscopy up to 1700 nm using a time-gated InGaAs/InP Single-Photon Avalanche Diode

Time-domain diffuse optical spectroscopy has become a powerful tool to study highly scattering media, mainly in the fields of non-invasive medical diagnostics and quality assessment of food and pharmaceutical products. Up to now this technique has been exploited mostly up to 1100 nm: we extend the spectral range by means of a continuously tunable pulsed laser source at a high repetition rate and a custom InGaAs/InP Single-Photon Avalanche Diode operated in time-gated mode, working up to 1700 nm. The characterization of the system is presented. As a first example of application, we measured the absorption spectrum of collagen powder in the range 1100 – 1700 nm, which could prove useful for breast density assessment.