Significance The atmospheric detection of the mesosphere (about 80-110 km) is of scientific research and application significance. There are many important spatial features and phenomena in this region, including the coldest altitude of the Earth's atmosphere (similar to 90 km), and special phenomena such as high-altitude noctilucent clouds, temperature inversion layer, and atmospheric metal layers also occur in this region. Gravity wave fragmentation makes the atmospheric disturbances in this region particularly intense, and the wind shear in this region becomes extremely intense. This region is also part of the atmospheric photochemical layer, and the atmospheric compositions have dramatic diurnal variations. With the development of aerospace, the influence of this region needs to be closely focused on. For example, suborbital flights (generally defined as 35 to 300 km to the Earth) involve this region, and these studies will lay a solid foundation for future suborbital commercial flights. This region has long been relatively unknown to humans because of the limitations of traditional detection methods. Fortunately, there are atmospheric metal layers in this region. As the cross section of resonance fluorescence scattering of metal atoms and ions is much larger than those of Rayleigh scattering and Raman scattering, it can be employed to detect low-concentration atmospheric components. In the past half century, by adopting the transition spectra of atoms and ions at specific wavelengths, the metal layer of the atmosphere has been detected by lasers with specific wavelengths and laser remote sensing technology. These metal atoms and ions are excellent tracers of atmospheric fluctuations, and many parameters such as atomic number density, temperature, and wind have been obtained. In recent years, with the discovery of thermospheric metal layers, the height range of atmospheric metal layers has been expanded, and the study of metal layers has been paid great attention to. Progress Based on the research of our team and collaborators, we introduce the development of atmospheric metal layer lidar and the current situation and trend of atmospheric metal layer detection by lidar. First, the dye laser opens the door to the atmospheric metal layer. Second, the sum frequency of the dye laser and YAG laser increases the laser energy further. Third, with pulsed dye amplifier employing dye as the working substance, directly amplifies the single-mode continuous seed laser into a high-power pulse laser. This meets the dual characteristics of high spectral resolution and sound center frequency stability of wind and temperature detection in metal layers. Fourth, narrow-band filtering technology extends lidar detection from night to all time. Fifth, a dye laser needs to change dye frequently with low single pulse energy, and all- solid-state laser solves this problem. Sixth, OPO lasers have many advantages such as high integration degree, good pump light spot, high single pulse energy, and further improved detection ability of atmospheric compositions. Additionally, we list the parameters of sodium atom, calcium atom and ion, iron atom lidar, and potassium atom lidar in four tables respectively. Conclusions and Prospects With the development of Q-switching, harmonic generation, tuning, high-power optical fiber devices, and other technologies, the pulse energy, stability, and operation convenience of lasers are constantly improving. In recent years, the simultaneous detection of multi-component density, temperature, and wind has become the trend. The multi-function lidar with high resolution and detection accuracy has been excavated and applied in China and abroad. In the future, the development and application of automated and intelligent lidar will promote satellite lidar, and in combination with ground-based lidar, more ion component detection will be possible to provide support for temperature and wind detection at higher altitudes. Finally, the cognition of chemical and physical processes in the upper atmosphere, and the coupling research on different regions of the ionosphere will be advanced.
