In the team’s setup, low-intensity pulses of visible laser light scan an object of interest. The laser fires a pulse at a given location until a single reflected photon is recorded by a detector; each illuminated location corresponds to a pixel in the final image.

Variations in the time it takes for photons from the laser pulses to be reflected back from the object provides depth information about the body — a standard way of revealing three-dimensional structure. However, the algorithm developed by Kirmani and his colleagues provides that information using one-hundredth the number of photons required by existing light detection and ranging (LIDAR) techniques, which are commonly used in remote mapping or measuring forest biomass, for instance.

via Stealth camera takes pictures virtually in the dark : Nature News & Comment.