We present laser-based spectroscopy in the mid-infrared spectral region inside novel anti-resonant (AR) hollow core fiber (HCF). AR-HCF used in this work has small (few dB/m) attenuation near 4 µm and exceptionally small bending losses. This gives perspective for compact all-fiber-based mid-infrared chemical sensors with optical path lengths of several meters. For gas sensing demonstration, a distributed feed-back (DFB) quantum cascade laser (QCL) operating near 4.54 μm and a 3.2-m-long fiber were used to detect nitrous oxide (N2O) and carbon monoxide (CO) using direct laser absorption spectroscopy (DLAS) and wavelength modulation spectroscopy (WMS).
A bismuth-doped fiber amplifier (BDFA) operating between 1650 nm and 1700 nm will be presented. This wavelength region is particularly interesting due to potential application is laser-based methane detection. However, typical output power from laser diodes operating in this spectral region is only between 5 and 15 mW which may limit sensitivity and/or detection range in some spectroscopic systems. Application of fiber amplifiers could help to overcome these limitations. BDFA presented in this paper provides output powers up to 80 mW at 1651 nm and 100 mW at 1687 nm. We analyze the noise at the output of the amplifier and demonstrate its application to photothermal spectroscopy of methane near 1651 nm.