Spectroscopic gas sensing was carried out by using an infrared hollow waveguide as a capillary flow cell. A ZnS-coated Ag hollow waveguide is generally the most suitable selection for use as a flow cell, since it exhibits high transmittance over the wide spectral range around 10 micrometers wavelength. For the corrosive gases that cause serious damage to the ZnS film, SiO2- or GeO2-based glass hollow waveguides are applicable. With these low-loss hollow waveguides, CH4, n-C4H10, NO2, and SO2 gases were measured successfully, and a fast response in gas detection as well as a remarkable reduction of gas consumption was demonstrated.
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