Trace-level detection of gases and vapours with mid-infra-red hollow waveguides

Mid-infra-red hollow waveguides have been applied to the detection of gases and vapours using a wavelength-tunable CO2 laser, The waveguides effectively operate as intrinsic sensors with the passage of small volumes of gas or vapour through the bore, an enhancement to analyte sensitivity has been investigated by several means using rigid and flexible hollow waveguides configured to provide extensions to the interacting optical path. The precision of measurement of absorbance is shown to reduce and then ultimately limit the minimum detection levels as the optical interaction path increases, Trace measurement of ethylene at sub-ppm levels (parts per million volume) is demonstrated with waveguide gas cells operating at elevated pressures over path lengths of several metres. For trichloroethylene and 2-furaldehyde, the minimum detection is less than 10 ppm under similar experimental conditions.