Highly sensitive and real-simultaneous CH4/C2H2 dual-gas LITES sensor based on Lissajous pattern multi-pass cell

Abstract

In this paper, a novel highly sensitive methane (CH4) and acetylene (C2H2) dual-gas light-induced thermoelectric spectroscopy (LITES) sensor based on Lissajous space-division multiplexed (LSDM) technology and trapezoidal-head quartz tuning fork (QTF) detector was reported for the first time. A theoretical LSDM model was established on the basis of three-mirror astigmatic multi-pass cell (MPC) and it was used to design a pair of Lissajous spot patterns with optical path length to volume ratios (OPL/Vs) of 13.5 cm−2 and 13.3 cm−2, respectively. Two self-designed trapezoidal-head QTFs with low resonant frequencies of less than 10 kHz and quality factor of ~12000 were adopted to enhance the detection ability. Two kinds of fiber amplifier, erbium doped fiber amplifier (EDFA) and Raman fiber amplifier (RFA), were combined to amplify the output power of two diode lasers to improve the excitation strength. After optimization, minimum detection limit (MDL) of 268.8 ppb and 91.4 ppb for real-simultaneous CH4 and C2H2 sensing were obtained, respectively. When the integration time of the system were 150 s and 100 s, the MDLs could be improved to 54.8 ppb and 26.1 ppb, accordingly. Further improvement methods for such sensor were discussed.

Keywords

• light-induced thermoelectric spectroscopy
• lissajous space-division multiplexed
• multi-pass cell
• quartz tuning fork
• dual-gas sensing