Big bore and extremely flexible mid-infrared hollow waveguide for gas absorption module

Abstract Big-bore, low-loss, and extremely flexible hollow waveguides were fabricated for mid-infrared spectroscopic gas sensing. The waveguide with inner/outer diameter of 1.4/2.0 mm can be curved with a bending radius as small as 1.4 cm A module of gas absorption cell for spectroscopic sensing was proposed with the hollow waveguide curved into a channeled substrate. Hollow waveguide with inner coatings of silver and silver iodide films attains low loss in the mid-infrared region for methane gas detection. Sensing properties for the module was experimentally discussed. Limit of detection of 6 ppm was obtained by using an FTIR (Fourier Transform infrared spectroscopy) system and DTGS (deuterated triglycine sulfate) detector. Comparisons were made to metallic hollow waveguide only with silver inner coating.