2-µm hybrid laser emitter for future carbon dioxide space-borne lidar measurement

TLDR: In this article, a DIfferential Absorption Lidar (DIAL) was developed for CO2 remote sensing using coherent detection, based on a pulsed hybrid laser emitter at 2.05 µm.

Abstract: We are developing a DIfferential Absorption Lidar (DIAL) for CO2 remote sensing using coherent detection, based on a pulsed hybrid laser emitter at 2.05 μm. In the 2 μm region, the R30 CO2 absorption line has been identified as one of the most promising for space-borne DIAL instrument to provide precise sounding of the atmospheric boundary layer where CO2 sources and sinks are located. In this paper, we present the Tm-doped all-fiber part of the emitter and we demonstrate its ability to measure the CO2 Volume Mixing Ratio (VMR) in the atmosphere. The lidar setup is presented, including the telescope, the heterodyne detection system and a spectral reference system used to infer the absolute frequency of the laser and the ON-line/OFF-line energy difference. We investigate an Integrated-Path-DIAL measurement on a range of 426 m. Results compare well with an in-situ reference sensor (Picarro probe), and the estimate statistics show good agreement with theoretical error calculations. This lidar demonstrator has been called HELENA (Hybrid Emitter Lidar for ENvironmetal Applications). Once completed, it will feature an hybrid emitter combining a semiconductor laser, a high-power Tm-doped fiber amplifier stage, and a final Ho:YLF crystal single-pass amplification stage. This combination aims at benefitting of the versatility, compactness and alignment easiness of a fiber amplifier on one hand, and of the high-peak power attainable with a solid-state amplifier on the other hand. It could allow overcoming the traditional Brillouin limit met in fiber amplifiers, without sacrificing much in compactness and robustness.