4.3 μm fiber laser in CO2-filled hollow-core silica fibers

Rare-earth-doped fiber lasers at 3-5 mu m can provide a variety of applications in defense, security, medicine, and so on. Limited by the maximum phonon energy of silicate glass host at room temperature, these lasers are normally based on soft-glass materials, e.g., fluoride or chalcogenide glass. However, due to the limited transparency of these fibers, until now these systems have only achieved coverage up to 3.92 mu m. Here, we report a CW fiber laser operating well beyond 4 mu m with significant power based on CO2-filled silica hollow-core fibers. By pumping via a homemade 2 mu m laser diode, similar to 82 mW optical power at 4.3 mu m was achieved at room temperature with a maximum laser efficiency similar to 19.3%. Our demonstration represents the longest-wavelength CW fiber laser to date, paving the way towards compact and high-power mid-infrared fiber lasers beyond the 4 mu m wavelength. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement