  We demonstrated a laser depth imaging system based on the time-correlated
single-photon counting technique, which was incorporated with a low-jitter
superconducting nanowire single-photon detector (SNSPD), operated at the
wavelength of 1550 nm. A sub-picosecond time-bin width was chosen for photon
counting, resulting in a discrete noise of less than one/two counts for each
time bin under indoor/outdoor daylight conditions, with a collection time of 50
ms. Because of the low-jitter SNSPD, the target signal histogram was
significantly distinguishable, even for a fairly low retro-reflected photon
flux. The depth information was determined directly by the highest bin counts,
instead of using any data fitting combined with complex algorithms. Millimeter
resolution depth imaging of a low-signature object was obtained, and more
accurate data than that produced by the traditional Gaussian fitting method was
generated. Combined with the intensity of the return photons, three-dimensional
reconstruction overlaid with reflectivity data was realized.
