Fig. 1. In the atmospheric environment of T = 296 K, P = 1013.25 hPa, the spectra of water vapor absorption cross section in the 935–936 nm region are obtained

Fig. 2. Block diagram of airborne vapor differential absorption Lidar system at NASA Langley Research Center^[29]

Fig. 3. Block diagram of an all-solid-state airborne vapor differential absorption lidar system for measuring the upper troposphere and stratosphere^[38]

Fig. 4. Block diagram of light source structure of WALES space project^[14]

Fig. 5. Comparison of DIAL data with radiosonde data^[16]

Fig. 6. Comparison diagram of water vapor measured by H₂O-DIAL and in-situ sensor^[41]

Fig. 7. A comparison of water vapor mixing ratio data detected by HALO, DLH and Sonde^[43]

Fig. 8. Block diagram of the fourth generation MPD system developed by Montana State University^[47]

Fig. 9. The correlation coefficient of the fourth generation MPD and the fifth generation MPD was compared with each other^[50]

Fig. 10. Curves of signal to noise ratio with height of λon and λoff in day and night respectively (a) and relative error of detecting water vapor concentration (b)

Fig. 11. Comparison of water vapor number density measurements between DIAL system and in-situ sensor^[52]

Fig. 12. Comparison of the volume humidity measured by the H₂O-DIAL system and the WXT-530 ^[53]

Fig. 13. Absorption cell frequency stabilization device for tunable CW Tm, Ho:YLF seed laser^[63]

Fig. 14. FMS frequency stabilization technology and offset locking technology combined frequency locking technology schematic diagram^[53]