A single external cavity laser-based sensor for simultaneous detection and quantification of atmospheric methane and water vapor

A single external cavity diode laser (ECDL)-based sensor system was developed for simultaneous measurements of methane and water vapor in the atmospheric air. A home-made continuous wave (CW) ECDL with a wavelength of similar to 1325 nm was employed to cover two absorption lines for different gas species. A high-finesse optical cavity composed of two high-reflectivity mirrors (R = 0.99927) was used to enhance the gas absorption in a space of 0.5 l. An isolated methane absorption line at 7552.74 cm(-1) and a common (non-isolated) absorption line of water vapor and methane 7552.81cm(-1) were utilized for simultaneous detection. A method was developed to calculate the water vapor concentration from these lines. To our knowledge, the method and the absorption lines used in the present paper were used for the first time for simultaneous measurement of the concentrations of atmospheric methane and water vapor.