Continuous Tb-doped fiber laser emitting at ∼5.25 µm

•Terbium doped chalcogenide glass fiber laser emitting 36 mW CW.•Fiber laser with wavelength exceeding 5 µm.•Multimode fiber lasing at TEM00 mode. The paper describes a chalcogenide glass fiber laser operating at the wavelength inaccessible to oxide and fluoride rare-earth doped fibers. The lasing fiber had 19 μm diam. selenide core doped with 2 × 1019 cm−3 of Tb3+ ions and 270 μm diam. undoped sulfide cladding. The pump source was a CW 1.98 µm Tm3+ fiber laser. Up to 36 mW TEM00 output was obtained in the 5.20–5.28 µm spectral band.