Near-Infrared C2H2 Detection System Based on Single Optical Path Time Division Multiplexing Differential Modulation Technique and Multi-Reflection Chamber

Abstract

A time division multiplexing differential modulation technique is proposed to address the interference problem caused by the fluctuation of laser light intensity in the single optical path detection system. Simultaneously, a multi-reflection chamber is designed and manufactured to further improve the system’s precision with an optical path length of 80 m. A near-infrared C2H2 detection system was developed. The absorption peak of the acetylene (C2H2) molecule near 1520 nm was selected as the absorption line. A laser driver is developed, and a lock-in amplifier is used to extract the second harmonic (2f) signal. A good linear relationship existed between C2H2 concentration and the 2f signal, and the correlation coefficient was 0.9997. In the detection range of 10–100 ppmv, the minimum detection limit was 0.3 ppmv, and the precision was 2%. At 50 ppmv, C2H2 and continuous detection for 10 h, the data average was 50.03 ppmv, and the fluctuation was less than ±1.2%. The Allan variance method was adopted to evaluate the long-term characteristic of the system. At 1 s of integration time, the Allan deviation was 0.3 ppmv. When the integration time reached 362 s, the Allan deviation was 0.0018 ppmv, which indicates the good stability of the detection system.

State-of-the-Art Laser Gas Sensing Technologies

“…The remaining papers report on the technical research of gas detection based on direct laser absorption spectroscopy [19][20][21][22][23][24][25]. The target analytes were acetylene (C 2 H 2 ) [19], methane (CH 4 ) [20], oxygen (O 2 ) [21], and 13 CO 2 / 12 CO 2 isotopic ratio [22]. The corresponding sensors were used for the monitoring of power plant exhausts [23] and vision imaging [24].…”

State-of-the-art Laser Gas Sensing Technologies

“…All the above review papers presented a full discussion with regard to the related technical field of gas sensing. The remaining papers report on the technical research of gas detection based on direct laser absorption spectroscopy [19][20][21][22][23][24][25]. The target analytes were acetylene (C 2 H 2 ) [19], methane (CH 4 ) [20], oxygen (O 2 ) [21], and 13 CO 2 / 12 CO 2 isotopic ratio [22].…”

Recent Advances in QEPAS and QEPTS Based Trace Gas Sensing: A Review

“…Due to the advantages of high selectivity and sensitivity, cost benefits, in-situ and non-invasiveness detection [1][2][3], optical gas sensors are widely used in numerous fields, such as combustion diagnostics, atmospheric monitoring, life sciences, planetary exploration, environmental monitoring, and early fire detection [4][5][6][7][8][9]. Many laser spectroscopy-based methods such as tunable diode laser absorption spectroscopy (TDLAS) [10][11][12][13][14][15], photoacoustic spectroscopy [16][17][18], and photothermal spectroscopy [19] have been adopted extensively.…”