Differential absorption lidar is an indispensable tool to measure atmospheric CO₂ for temporal and spatial distribution. The 2.0 μm wavelength Ho:Tm:YLF/Ho:Tm:LuLiF lidar were used for remote sensing atmospheric CO₂ with heterodyne receiver. The KTP parametric oscillator was injected into the seeds, and a differential absorption lidar (DIAL) system of 1.6 μm by using the photon counting technique to profile the atmospheric CO₂ in the troposphere under 7 km. Modulation continuous wave seed laser intensity and the integral path differential absorption lidar, common 1.6 μm optical fiber amplifier, and the use of correlation detection technique, have unique advantages and characteristics in the detection of atmospheric CO₂ column concentrations. The space program for detecting atmospheric CO₂ column concentrations is NASA's ASENDS (active sensing of CO₂ emission over nights, days, and seasons) mission which adopts the method of pulse and integral path differential absorption. The absorption of CO₂ gas cell as a reference to stabilize seed light frequency and the precise control of cavity length lock the on-line wavelength of transmitter, is the key technique for DIAL to measure atmospheric CO₂.