Multi-component gas measurement aliasing spectral demodulation method for interference separation in laser absorption spectroscopy

The interference between overlapping gas absorption lines often occurs in the measurement of multi-component gas mixture with using laser absorption spectroscopy. It has become a “bottleneck” problem in many application areas. Therefore, in this paper, we take the measurement of CH4 and CO gas mixture as an example to develop a dual-gas sensor using tunable diode laser absorption spectroscopy with a novel multi-component gas measurement aliasing spectral demodulation method for interference separation. With the assistance of the above methods, the concentrations of CO and CH4 are inverted by analyzing the severely aliased second harmonic signal (2f) in the coexistence of trace CO and CH4 with high concentration. Experiments have verified that precise measurement results can be obtained, whether it is to measure individual CO or CH4, or to measure the gas mixture. Even in the presence of 1.6 × 104 ppm CH4, the measurement error of 10 ppm CO is no more than 0.9 ppm. And, the response time of this sensor for CO and CH4 detection are both ~17 s. Finally, the repeatability of this sensor is validated by continuous detection analysis, which indicates that measurement precision is 0.10 ppm for 20 ppm CO and 1.02 ppm for 200 ppm CH4, respectively. Therefore, this novel processing method avoids the shortage of low-pressure control without adding any hardware, which is more universal and convenient.