Hollow Waveguide Gas Sensor for Mid-Infrared Trace Gas Analysis

A hollow waveguide mid-infrared gas sensor operating from 1000 cm^-1 to 4000 cm^-1 has been developed, optimized, and its performance characterized by combining a FT-IR spectrometer with Ag/Ag-halide hollow core optical fibers. The hollow core waveguide simultaneously serves as a light guide and miniature gas cell. CH^-4 was used as test analyte during exponential dilution experiments for accurate determination of the achievable limit of detection (LOD). It is shown that the optimized integration of an optical gas sensor module with FT-IR spectroscopy provides trace sensitivity at the few hundreds of parts-per-billion concentration range (ppb, v/v) for CH^-4.