Compact dual-wavelength system for time-resolved diffuse optical spectroscopy

Abstract

We present a compact instrument for time-resolved diffuse optical spectroscopy based on two pulsed diode lasers, a Silicon PhotoMultiplier working in single-photon regime and a custom-made Time-to-Digital Converter. The temporal width of the Instrument Response Function is narrower than 300 ps (Full-Width at Half Maximum) and the time measurement unit exhibits 10 ps temporal resolution with a Full Scale Range of 80 ns. The laser pulses are injected into the sample through two 400 μm core optical fibers and re-emitted light is collected by 1 mm core plastic optical fiber aligned with detector active area. The instrument is housed in a compact 200 × 160 × 50 mm3 metal case, weighs less than 2 kg and requires a single 15 V DC voltage power supply, with a power consumption lower than 10 W, thus being suitable for battery operation. The long-time measurement stability makes the system ideal for monitoring applications on the field, where state-of-the-art bulky time-resolved systems cannot be exploited.