|Abstract:||Greenhouse gases were monitored on an open-path over kilometer length with calibrated wavelength modulation spectroscopy (WMS). A movable platform was developed capable of detecting atmospheric variations of the concentrations of methane and carbon dioxide. Two single-mode continuous commercial Distributed Feedback Diode Lasers (DFB-DL) with a fiber tail were employed as the laser sources with the wavelengths ~1654 nm and ~1602 nm (corresponding to the absorption features of methane and carbon dioxide, respectively) and the output powers of 10 mW each. These near-IR wavelengths give advantages of weaker interference of water absorption and readily available emitting and receiving equipment developed for applications at telecommunication wavelengths. The intensity modulation caused by turbulence was also observed. We realized an automated continuous monitoring of methane for more than 30 hours . Similar measurements of carbon dioxide were performed for about 10 hours. The results show that the detection limits of methane and carbon dioxide are ~2 ppb and ~20 ppm with integration times of 60 seconds and 20 seconds, respectively. The developed sensor is a promising tool for monitoring of greenhouse gases.
This work was supported by the Robert A Welch Foundation (grant No A1546) and a T3 grant from Texas A and M University and Open Fund of State Key Laboratory of Applied Optics (SKLA02020001A12).
 J. Xia, Feng Zhu, Sasa Zhang, Alexandre Kolomenskii, Jian Dong, Kunihiro Okada, James Strohaber, Hans. A. Schuessler, Probing greenhouse gases in turbulent atmosphere by long-range open-path wavelength modulation spectroscopy, Optics and Lasers in Engineering, 117, 21-28 (2019).
 Jinbao Xia: State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences Changchun, 130033, China