Research of TDLAS methane detection system using VCSEL laser as the light source

Compared with the DFB laser, the TDLAS laser gas detecting system using the VCSEL laser as the detecting light source has the advantage of low power consumption. According to the characteristic of the low power TDLAS gas detection signal, combined with the characteristics of modulation VCSEL laser source, a laser driver, signal acquisition and processing were designed, and a low-power TDLAS methane (CH₄) gas detector based on WMS was designed. The absorption peak of CH₄ molecule near 1653.7 nm was selected as the absorption line, and the second harmonic (2f) signal was extracted by a lock-in amplifier. The response of different concentrations of CH₄ detection was studied experimentally, and the 2f signal's amplitude was recorded and linearly fitted. The results show that the CH₄ concentration has a good linear relationship with its 2f signal's amplitude, and the linearity is 0.9998. Accuracy of the detection system is better than 10% in the range of 50 - 500 ppmv, and the detection limit is 10 ppmv. With the long-term detection of 250 ppmv of CH₄ for 10 h, the fluctuations are less than ± 2.4%. Allan deviation analysis was introduced. When the initial integration time was 1 s, the Allan deviation was 9.9 ppmv. When the integration time reached 359 s, the Allan deviation was 0.06 ppmv, which indicated the good stability of the system.