Taking really detailed 3D images from afar can be difficult without multiple cameras, but it is possible using individual particles of light, called photons. A team of researchers have now quadrupled the range of this technique, perhaps paving the way for creating such images from aeroplanes.
Feihu Xu at the University of Science and Technology of China and his colleagues used an existing single-photon version of a method called lidar, which stands for light detection and ranging, to take their images. They used a low-power laser to bounce light off an object, along with a powerful detector to catch one photon at a time.
Using a single photon for imaging makes it easier for the detector to determine which photons came from the laser and which are background light that should be discarded. The team developed an algorithm that is able to do this with increased efficiency. 鈥淚maging with single photons can provide the high sensitivity, which permits imaging over long ranges,鈥� says Xu.
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The amount of time the photon takes to travel to the object and back to the camera indicates how far it has travelled. Each photon can only measure a single point, but scanning the beam of the laser across an object builds up a 3D representation.
The previous distance record for this kind of imaging was about 10 kilometres between the target and the laser. Xu and his colleagues extended that to 45 kilometres, placing their equipment on the 20th floor of a building across a river from the building they imaged. Despite the distance, they were able to pick out individual windows of the target building both during the daytime and at night.
This kind of 3D imaging could be used for surveillance from afar, perhaps from an aeroplane. Eventually when the distance is increased, either with more sensitive cameras or a more powerful algorithm to compile the data into an image, it could even be used to take 3D images from satellites, Xu says.
Journal reference: Photonics Research,
