8.6 W Single-Frequency Fluoride Fiber MOPA at 3.5 μm

Single-frequency laser sources emitting in the 3-5 μm mid-infrared wavelength regime that overlaps with both the atmosphere windows and the molecular fingerprint region, have been established important tools for communication, spectroscopy and sensing. Demonstrations of such lasers usually rely on optical parametric oscillators (OPOs), however, which usually exhibit bad beam quality due to the absence of waveguide. Alternatively, mid-infrared laser can also be directly obtained via the stimulated emission in rare-earth-doped fiber lasers which benefit advantages in compactness, thermal management and beam quality. However, the efficient single-frequency output has seldom been demonstrated due to the lack of fiber devices and difficulties with the fiber handling, and the output power of reported single-frequency mid-infrared fiber lasers remain tens of milliwatts. Last year, our group demonstrated the first 105 mW single-frequency output from a 3.5 μm Er-doped ZBLAN fiber laser [1], whereas further power scaling of single-frequency output was limited by the insufficient frequency selection of the fiber oscillator. Here, we boosted the hundred-milliwatt single-frequency output from the fiber oscillator to multi-watt level based on a master-oscillator power-amplifier (MOPA) configuration. The maximum output power of the continuous-wave single-frequency laser reached 8.6 W, which is comparable to the highest level generated from the OPOs [2].