Non-Contact Inclusion Detection in Food Through a Single-Photon Time-of-Flight Imager

We present a non-contact and non-invasive diffuse optical imaging system, based on an array of 32 × 32 single-photon avalanche diodes and time-to-digital converters, able to measure the time-of-flight of single photons, with 350-ps resolution. Measurements using continuous-wave (CW) and time-domain (TD) techniques demonstrate the possibility to identify the presence of absorbing inclusions (not visible by eye because of high scattering) within a diffusive media in transmittance geometry, with no contact with the sample. Thanks to the 1024 fully independent and concurrent time-resolved detection points, TD acquisitions achieve better resolution than CW ones, with the same measurement time. Provided that the investigated medium presents adequate thickness and transmissivity at the wavelengths of interest in order to allow sufficient light penetration, the system can be employed as a quick imaging device in food industries for non-destructive quality control.