Dual-Gas Sensor of CH4/C2H6 Based on Wavelength Modulation Spectroscopy Coupled to a Home-Made Compact Dense-Pattern Multipass Cell

Abstract

A sensitive dual-gas sensor for the detection of CH₄ and C₂H₆ is demonstrated. Two tunable semiconductor lasers operating at 1.653 μm (for CH₄ monitoring) and 1.684 μm (for C₂H₆) were used as the light source for spectroscopic measurements of CH₄ and C₂H₆. Long-path absorption in a home-made compact dense-pattern multipass cell (L_eff = 29.37 m) was employed, combined with wavelength modulation and second harmonic detection. Simultaneous detection of CH₄ and C₂H₆ was achieved by separated wavelength modulations of the two lasers. Modulation frequencies and amplitudes were optimized for sensitivity detection of CH₄ and C₂H₆ simultaneously. The dual-gas sensor exhibits 1σ detection limits of 1.5 ppbv for CH₄ in 140 s averaging time and 100 ppbv for C₂H₆ in 200 s.