Opo lidar sounding of trace atmospheric gases in the 3 – 4 μm spectral range Oleg A. Romanovskii, Sergey A. Sadovnikov, Olga V. Kharchenko and Semen V. Yakovlev EPJ Web Conf., 176 (2018) 05016 Published online: 13 April 2018 DOI: 10.1051/epjconf/201817605016