Physicists have demonstrated the operation of lidar, which is able to build three-dimensional detailed (with a resolution of up to several decimeters thick) images of objects at a distance of 45 kilometers and to work in conditions of high noise and weak (of the order of one photon per pixel) signal. According to the authors, in the future, the proposed technology can provide detailed images at the single-photon signal at distances of up to several hundred kilometers — that is, on extra-long distances for lidar. Article published in the journal of Photonic Research.
Lidar is a device that allows you to obtain information about distant objects by means of optical radiation. The main elements of such a device are the emitter and the receiver. The light from the emitter is reflected, when faced with an obstacle, and (in a somewhat distorted form, as on the way the scattering occurs) is returned to the receiver by the time interval between generating and recording beam to calculate the distance to the object from which light was reflected. Sending rays in many directions, it is possible thereby to reconstruct three-dimensional images of opaque objects.
At far enough distances (order of kilometers) lidars are faced with a problem: the signal radiation twice (for forward and reverse paths) is dissipated in the extended environment, separating the object and the device, and the receiver thus detects the unnecessary light that does not carry useful information. The situation arises when one pixel of the image formed have very few reflected photons and many times greater than the background — in such circumstances, it is difficult to distinguish the signal among the noise. Despite the fact that there are algorithms for filtering and processing data, to combine enough high-quality single-photon image and the lidar stand-off is still difficult.
Scientists from the University of science and technology of China under the leadership of Zheng Ping Li (Zheng-Ping Li ) and Xin Huang (Huang Xin) produced a long-range lidar and tested single photon registration at distances of tens of kilometers. As the emitter physicists have used an infrared laser (wavelength 1550 nm) is allowed to combine safety device for vision with good transparency of the atmosphere (the proportion of radiation that passes air for this wavelength is comparable to the same degree for the visible range) and thus reduce the effect of sunlight (the intensity at the earth’s surface in the infrared range is 2-3 times lower than in the visible).