摘要： 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 CH4 through a gas mixture with relatively high water content, such as when studying gas emission from methane-rich thermokarst lakes in northern regions. To this end, we present a tunable all-fiber laser emitting near 3.43 μm and operating at high average power. The laser design (Fig. 1) is based on an all-fiber dual-pumping scheme [3], which combines core-pumping at 1976 nm with clad-pumping at 976 nm in a single-mode erbium-doped fluoride glass fiber to reach, in the present case, up to 3 W of output power at the desired wavelength. The laser cavity itself is delimited by two fiber Bragg gratings (FBG): a highly-reflective (HR) FBG at the input, which has a narrow bandwidth to dictate the laser wavelength, and a lowly-reflective (LR) FBG at the output, which has a large bandwidth to accommodate shifts of the HR FBG. Tuning of the laser cavity is achieved by mechanically stretching (i.e. lengthening) the HR FBG via the beam bending technique [4]. The HR FBG is nested within an Invar-based metallic groove and fixed using a polymer of sufficient elasticity, the groove is then deformed using a piezoelectric actuator (PA), allowing for rapid and precise wavelength tuning over a wavelength range of a few nanometers. Figure 2 compares normalized spectra of the laser emission at various commanding voltages for the PA along with the absorption spectrum of methane as given by the HITRAN database [1]. As can be seen on Fig.2, the presence of consecutive extrema (min-max) allows for quick referencing of the measurement during each tuning cycle. Early gas cell experiments and further engineering refinement show good promise for future deployment in northern regions by climate scientists.