Methane, Ethylene, and Ethane Detection by Differential Helmholtz Resonance Spectroscopy Using a 3345 nm Mid-Infrared Tunable Diode Laser Source

Gas detection based on photoacoustic spectroscopy (PAS) has attracted extensive attention due to its high sensitivity and large range of linearity. Herein, to achieve the simultaneous detection of the light carbon gases (CH4, C2H4, and C2H6), a gas detection system was constructed using a single mid-infrared tunable diode laser (central wavelength 3345 nm) source based on differential Helmholtz resonance spectroscopy (DHRS). The detection parameters (driving current, modulation depth, phase angle, etc.) were optimized under ambient pressure using the 1f demodulation method. With an integration time of 2 s, the detection limit reached 98.8 ppb, 252 ppb, and 33 ppb for methane, ethylene, and ethane, respectively. The validation test of the three-component mixture shows that the cross-interference can be effectively reduced by multiwavelength linear regression, and single wavelength linear regression causes large errors in the quantification of methane and ethylene.