This paper highlights a significant advance in time-of-flight depth imaging: by using a scanning transceiver which incorporated a free-running, low noise superconducting nanowire single-photon detector, we were able to obtain centimeter resolution depth images of low-signature objects in daylight at stand-off distances of the order of one kilometer at the relatively eye-safe wavelength of 1560 nm. The detector used had an efficiency of 18% at 1 kHz dark count rate, and the overall system jitter was ~100 ps. The depth images were acquired by illuminating the scene with an optical output power level of less than 250 µW average, and using per-pixel dwell times in the millisecond regime.
McCarthy, A., Krichel, N. J., Gemmell, N. R., Ren, X., Tanner, M. G., Dorenbos, S. N., Zwiller, V., Hadfield, R. H., & Buller, G. S. (2013). Kilometre-range, high resolution depth imaging using 1560 nm wavelength single-photon detection. Optics Express, 21(7), 8904-8915. https://doi.org/10.1364/OE.21.008904