Abstract
In this paper, we present an innovative instrument for near-infrared time-resolved spectroscopy. The system is based on eight custom-designed pulsed diode lasers emitting at different wavelengths in the near-infrared region (635–1050 nm), all exhibiting an average optical power higher than 1 mW at 40 MHz pulse repetition rate, two custom-made single-photon detectors based on wide-area silicon photomultipliers and two time-measurement units based on a custom time-to-digital converter with 10 ps timing resolution. The system instrument response function has a width narrower than 160 ps (fullwidth at half-maximum) and stability better than ±1% for several hours for all the wavelengths. All the components of the instrument were designed in order to be compact. The entire system will be hosted in a standard 19 inches, 5U rack case (size 48 × 38 × 20 cm3 ). The system communicates with the external computer through a USB 2.0 link and is designed to be employed in a clinical environment. The proposed instrument, thanks to the reduction of its cost and dimensions, paves the way to a wider diffusion of multiwavelengths near-infrared time-resolved spectroscopy systems.
Highlights
O VER the last few years, the interest towards photonic instruments have seen an exponential growth in several fields, from automotive to industrial automation, chemistry, biomedicine and many others
The easiest implementation of Diffuse Optics (DO) techniques is based on a Continuous Wave (CW) light and detection, and the low system complexity guarantees low cost and small dimensions, leading to a wide diffusion in both the clinical and the commercial fields, where compact systems are currently under development to be equipped in wearable devices [9]
To limit the measurement timing jitter added to the Distribution of Time-Of-Flight (DTOF) curves, the detector Single-Photon Timing Resolution (SPTR) should be in the order of tens of picoseconds, while the Photon Detection Efficiency (PDE) must be as high as possible in the near-infrared range in order to improve the signal-to-noise ratio
Summary
O VER the last few years, the interest towards photonic instruments have seen an exponential growth in several fields, from automotive to industrial automation, chemistry, biomedicine and many others. The easiest implementation of DO techniques is based on a Continuous Wave (CW) light and detection, and the low system complexity guarantees low cost and small dimensions, leading to a wide diffusion in both the clinical and the commercial fields, where compact systems are currently under development to be equipped in wearable devices [9]. This approach has several drawbacks [10], as the impossibility, using a single source-detector pair, to distinguish between photon scattering and absorption phenomena within the sample and a limited depth sensitivity and selectivity [11], [12]. A wide range of wavelengths permits better discrimination between various constituents like lipids, collagen and water, in addition to oxygenated and de-oxygenated hemoglobin, providing more information on the sample
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