Low-loss Fused Silica Hollow-Core Fiber Delivery of Mid-infrared Light at 6-μm

Mid-infrared (MIR) lasers at a wavelength of $\sim 6\mu \mathrm{m}$ are extremely valuable for medical, chemical, and industrial, applications. In particular, they have been shown to be in the optimal wavelength region to minimize collateral damage in soft tissue ablation using free-electron lasers [1]. Quantum cascade lasers (QCLs) are a potentially superior alternative, being simpler, more compact, and lower cost. However, as the silica glass used in traditional optical fibers is opaque at these wavelengths, it is difficult to find flexible, low-loss, single-mode fiber delivery solutions, limiting the use of these wavelengths in applications. Silica hollow-core fibers (HCFs) are a very attractive solution as they combine the maturity of silica fiber fabrication techniques with hollow-core transmission [2]. Previously Kolyadin et al reported an 8-capillary silica HCF guiding light up to 7.9 $\mu\mathrm{m}$ but with a loss of>20 dB/m at $\sim 6\mu \mathrm{m}$ [3].