Tunable All-Fiber Laser for Remote Sensing of Methane Near 3.4 μm

The mid-infrared (MIR) region of the optical spectrum has drawn considerable scientific interest in the past few years. Indeed, several molecules relevant to medical or environmental conundrums exhibit strong absorption lines in this region: for instance, methane lines in the MIR are up to 100 times stronger than in the near-infrared [1]. In turn, fiber lasers have long stood as prime candidates for remote gas detection in outdoor environments, given their exemplary robustness, power scaling and beam quality. However, while several previous contributions have targeted methane bands under 3.3 μm in wavelength [2], little work has been done to push fiber laser detection tools past 3.4 μm, where methane absorption lines are mostly decoupled from the absorption spectra of water and other atmospheric constituents. This is especially relevant when probing CH
₄
through a gas mixture with relatively high water content, such as when studying gas emission from methane-rich thermokarst lakes in northern regions.