Abstract
This work reviews physical concepts, technologies and applications of time-domain diffuse optics based on time-gated single-photon detection. This particular photon detection strategy is of the utmost importance in the diffuse optics field as it unleashes the full power of the time-domain approach by maximizing performances in terms of contrast produced by a localized perturbation inside the scattering medium, signal-to-noise ratio, measurement time and dynamic range, penetration depth and spatial resolution. The review covers 15 years of theoretical studies, technological progresses, proof of concepts and design of laboratory systems based on time-gated single-photon detection with also few hints on other fields where the time-gated detection strategy produced and will produce further impact.
Highlights
Diffuse optics (DO) is a branch of optics which aims to study the optical properties of a diffusive medium using light in the near-infrared spectral window, that is the wavelength range where the water absorption is negligible [1]
Apart from traditional photomultiplier tubes (PMTs) [32] and silicon photomultipliers (SiPMs) [33], which at present cannot be time-gated, the other detectors typically employed in TD-DO, such as intensified charge coupled device (ICCD) [28,34], microchannel plates (MCP) [35], streak cameras [36] and single-photon avalanche diodes (SPADs), [37] can be used in the TG modality [31]
The typical single-photon timing response shape of a SPAD is given by two main contributions: (i) a sharp Gaussian peak due to photons directly absorbed in the depleted region of the SPAD p-n junction and (ii) a slow decaying exponential tail starting about one order of magnitude below the response peak
Summary
Diffuse optics (DO) is a branch of optics which aims to study the optical properties of a diffusive medium using light in the near-infrared spectral window, that is the wavelength range where the water absorption is negligible [1]. Apart from traditional photomultiplier tubes (PMTs) [32] and silicon photomultipliers (SiPMs) [33], which at present cannot be time-gated, the other detectors typically employed in TD-DO, such as intensified charge coupled device (ICCD) [28,34], microchannel plates (MCP) [35], streak cameras [36] and single-photon avalanche diodes (SPADs), [37] can be used in the TG modality [31] In almost all these detectors, performances are limited by early photons impinging onto the detector, increasing dramatically the background noise or even damaging the detector.
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