3.1 W mid-infrared fiber laser at 4.16 µm based on HBr-filled hollow-core silica fibers.

We present the characteristics of a continuous-wave (CW) mid-infrared fiber laser source based on HBr-filled hollow-core fibers (HCFs) made of silica. The laser source delivers a maximum output power of 3.1 W at 4.16 µm, showing a record value for any reported fiber laser beyond 4 µm. Both ends of the HCF are supported and sealed by especially designed gas cells with water cooling and inclined optical windows, withstanding higher pump power accompanied by accumulated heat. The mid-infrared laser exhibits a near-diffraction-limited beam quality with a measured M of 1.16. This work paves the way for powerful mid-infrared fiber lasers beyond 4 µm.