A Quantum Detector System For Hybrid Time-domain Diffuse Optics

Diffuse optics (DO) enables non-invasive monitoring of oximetry and flowmetry by combining time-domain near-infrared spectroscopy (TD-NIRS) [1] and time-domain diffuse correlation spectroscopy (TD-DCS) [2]. These methods require detectors with high near-infrared quantum efficiency (QE), excellent temporal resolution, and low dark count rate (DCR). We present a system based on superconducting nanowire single-photon detectors (SNSPDs) that fulfils these needs. In single-mode configuration at 785 and 1064 nm, QE exceeds 70%, DCR stays below 10 cps, and jitter remains under 40 ps.

 

To demonstrate suitability for TD-NIRS, we measured absorption spectra of tissue-mimicking liquid phantoms and successfully retrieved their optical properties thanks to the SNSPDs’ high dynamic range. For TD-DCS, we conducted an in-vivo occlusion experiment at 1050 nm on a healthy volunteer. A 3-minute baseline was followed by 3 minutes of cuff-induced blood flow blockage and subsequent release. The intensity autocorrelation functions clearly distinguished each stage and changes in decay rate reflected blood-flow variations. These results confirm that SNSPDs enable high-performance hybrid time-domain diffuse optics.