A technologically simple optical fiber cross-section structure with a negative-curvature hollow-core has been proposed for the delivery of the CO2 laser radiation. The structure was optimized numerically and then realized using Te20As30Se50 (TAS) chalcogenide glass. Guidance of the 10.6 µm СО2-laser radiation through this TAS-glass hollow-core fiber has been demonstrated. The loss at λ=10.6 μm was amounted ~11 dB/m. A resonance behavior of the fiber bend loss as a function of the bend radius has been revealed.

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In this paper we consider mid-infrared Raman lasers based on gas-filled hollowcore silica fibers and provide theoretical and experimental analysis of factors that limit the efficiency and output power of these lasers. As a result, we realized an efficient ns-pulsed 4.42 µm Raman laser based on an 1 H 2 -filled revolver silica fiber. Quantum efficiency as high as 36 % is achieved, and output average power as high as 250 mW is demonstrated. The possibilities of further improving the laser efficiency are discussed.