Hollow-Core-Fiber Delivery of Broadband Mid-Infrared Light for Remote Multi-Species Spectroscopy

Mid-infrared (mid-IR) light provides a means to identify molecules using ro-vibrational spectroscopy. Where measurement is required in a remote or hazardous environment, fibre delivery is convenient, but is limited by the scalability of fluoride and chalcogenide fibres to only a few meters in length. Low-loss mid-IR hollow-core fibres (HCFs) have been reported [1] , [2] , with losses at 3.1m of 18 dB km -1 [3]. Here, we report fibre-delivered multi-species mid-IR spectroscopy, with broadband 2850-3150 cm -1 light routed to a remote gas cell via HCF. By using Fourier-transform spectroscopy we achieve resolutions of 0.05 cm -1 and in-fibre concentration measurements of contaminants H 35 Cl and H 37 Cl with 5-ppb precision. High-resolution multi-species fitting is used to mitigate spectroscopic interference between species, enabling spectroscopy in a gas cell after the fibre.