Its principle is the same as that of radio radar. After the laser is aimed at the target and launched, its round-trip time is measured, and then multiplied by the speed of light to obtain the round-trip distance. Because the laser has the advantages of high directivity, high monochromaticity and high power, these are very important for measuring long distances, determining the orientation of the target, improving the signal-to-noise ratio of the receiving system, and ensuring the measurement accuracy. increasingly received attention. The lidar developed on the basis of the laser rangefinder can not only measure the distance, but also measure the azimuth, speed and acceleration of the target. Radar, ranging from 500 to 2000 kilometers, the error is only a few meters. Not long ago, the LDM series ranging sensors developed by some R&D centers can reach micron-level accuracy in the measurement range of thousands of meters. Ruby lasers, neodymium glass lasers, carbon dioxide lasers, and gallium arsenide lasers are often used as light sources for laser rangefinders.