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Hollow-core waveguide for single-mode laser beam propagation in the spectral range of 3.7-7.3 μm

We report the first demonstration of single-mode laser beam delivery in hollow-core waveguides (HCWs) operating in the 3.7-7.3 μm spectral range. We investigated the transmission properties of HCWs with 200 μm bore diameter and internal coatings properly designed to enhance the spectral response in the spectral range of 3-12 μm. We achieved single mode output throughout the 3.7-7.3 μm range. We measured a coupling efficiency < 90% and transmission losses as low as 1 dB, when using a 15 cm-long fiber at 3.7 μm under optimized coupling conditions between input beam and HCW.