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

Abstract

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 $$\sim$$ 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 $$7552.74 \hbox { cm}^{-1}$$ and a common (non-isolated) absorption line of water vapor and methane $$7552.81\hbox {cm}^{-1}$$ 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.