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Wavelength stabilization for a pulsed laser presents more challenges than that of continuous wave laser. We have developed a simple and efficient long-term wavelength drifts compensation technique for tunable pulsed dye lasers (PDL) applied in sodium detection lidar system. Wavelength calibration and locking are implemented by using optogalvanic (OG) spectroscopy in a Na hollow cathode lamp (HCL) in conjunction with a digital control software. Optimization of OG signals for better laser wavelength discrimination and feedback control is performed. Test results indicate that locking the multimode broadband PDL to the Na atomic transition corresponding to 589.158 nm is well achieved although the temperature in the laboratory is unstable. Through active compensation, the maximum wavelength drift is reduced from over 5 pm to 0.42 pm in 10 h and the maximum wavelength drift rate of the PDL is improved from 3.3 pm/h to 0.3 pm/h. It has been used to efficient sodium resonance fluorescence lidar detection. This technique is economical and easy to implement, and it provides flexible wavelength control and allows generalization for some other applications which require the wavelength of tunable pulsed lasers to be fixed at an atomic resonance transition references. [ABSTRACT FROM AUTHOR]

• A new Ni lidar has been designed and deployed at Yanqing station. This lidar has three advantages: first, the lidar employs 532 nm laser light to pump a near-IR laser dye with a high conversion efficiency and long life (dye replacement every 36 hours), which is much better suited to long-term observations; second, frequency doubling the IR laser beam avoids disturbances by receiving backscatter of Amplified Spontaneous Emission (ASE) of the dye laser.; third, this new Ni lidar makes use of narrow bandwidth interference filters. The narrow bandwidth filters better discriminate against background light. • The lidar measurements of Nickel layers have been made in Yangqing from 3 April to 31 December 2019 (25 days in total). This demonstrates the stability of the lidar for making continuous Ni measurements over an extended period, enabling the first investigation of night-time and seasonal density variation of the Ni layer. The Ni density results are similar to that reported by Gerding et al. [2018] and the WACCM-Ni model [Daly et al., 2020]. • For the first time, we used the high altitude Ni lidar to determine the branching ratios of three different optical transition from Ni in the 3d9(2D)4s3D3 state (excited at 341 nm), and showed that these branching ratios are very close to the theoretical values. Ni atoms, produced in the Earth's upper atmosphere by meteoric ablation, are challenging to measure by lidar because the Ni atom density is low, the resonance scattering cross section is relatively small, and the transitions occur in the near-UV around 340 nm where absorption by the stratospheric ozone layer starts to become significant. A new Ni lidar has been designed and deployed at Yanqing station (4 0 ∘ N , 11 6 ∘ E) Beijing, China over the period from 3 April 2019 to 31 December 2019. The combination of a frequency-doubled near-IR laser and narrow bandwidth filters enables stable and continuous operation. From 25 nights of measurements, the Ni peak density ranges from 98 to 460 cm−3 with the peak altitude between 80 and 88 km; the average peak density is 258 ± 115cm−3. The average column abundances of Nickel varied between 1.52 × 108 and 6.0 × 108 cm−2 between mid-summer and mid-winter. An experiment was also carried out using the Ni lidar to determine the spectroscopic branching ratios from the excited Ni(3F 4) state into 3 lower states; very close agreement with the literature values were obtained. [ABSTRACT FROM AUTHOR]