Thanks to recent progresses in the fabrication of sub-µm domain gratings in Rb-doped KTiOPO<inf>4</inf> [1], backward quasi-phase matching can be precisely engineered to produce specific wavelengths for absorption spectroscopy applications [2]. As a consequence, the Backward Wave Optical Parametric Oscillator (BWOPO) is raising interest for application requiring precisely controlled narrow-line infrared radiation such as Differential Absorption LIDAR (DIAL). In this research work we study the fine wavelength and linewidth properties of a BWOPO designed to address the CO<inf>2</inf> R30 absorption line at 2051 nm, which is one of the most suited ones for CO<inf>2</inf> lidar probing from space [3]. For this purpose, we implemented the experimental set-up described in Fig.1(a) hereafter.