Highly sensitive and real-simultaneous CH<sub>4</sub>/C<sub>2</sub>H<sub>2</sub> dual-gas LITES sensor based on Lissajous pattern multi-pass cell

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…