High-efficiency longwave 2085 nm laser output in low-loss Ho3+-doped fluorotellurite glass fiber by 1976 nm in-band pumping.

• Fabricated Ho3+-doped fluorotellurite glass fiber with a low loss of 0.59 dB/m. • The high-power laser irradiation tolerance of the fluorotellurite fiber was verified. • Achieved a 2085 nm single-mode laser output with 90.4 % slope efficiency. • Discussed the functional relationship between fiber length and laser performance. High-gain Ho3+-doped optical fibers are imperative exigency for > 2 µm single-mode fiber lasers. Here, we have successfully developed and fabricated a low-loss Ho3+-doped fluorotellurite glass fiber. The high-power laser irradiation tolerance of the fiber was verified, and the end face of Ho3+-doped fluorotellurite glass fiber remained undamaged under a ∼ 70 W of 981 nm CW laser irradiation. An unsaturated maximum 6.35 W@2085 nm single-mode laser output with a slope efficiency of 90.4 % was achieved in a 25 cm short fiber by homemade 1976 nm laser in-band pumping. To the best of our knowledge, this is currently the highest slope efficiency reported for Ho3+ doped fluorotellurite fiber lasers to date in a space laser cavity. The effects of the fiber length on the laser threshold, slope efficiency, and output wavelength are further discussed. This work offers valuable insights into prospective candidate materials and scheme designs for the future development of high-efficiency, long-wavelength mid-infrared ∼ 2.1 μm fiber lasers. [ABSTRACT FROM AUTHOR]