Differential laser-induced thermoelastic spectroscopy for dual-gas CO2/CH4 detection

A novel differential laser-induced thermoelastic spectroscopy (D-LITES) was demonstrated. In D-LITES, one probe and one control laser beam with different modulation phases were combined to generate two quartz tuning fork (QTF) mechanical oscillations, which are π out of phase. The powers of the two lasers were adjusted to balance out the background noise. The differential signal was acquired by demodulating the QTF piezoelectric signal. The D-LITES sensor had a compact and cost-effective one-path configuration and was able to realize dual-gas detection. Carbon dioxide (CO2) and methane (CH4) were chosen as target gases to verify the D-LITES sensor performance. With the D-LITES technique, the background noise was greatly suppressed. The minimum detection limit (MDL) was improved by 9 times from 260 ppm to 29 ppm and 7.13 times from 0.385 ppm to 0.054 ppm for CO2 and CH4 detection, respectively.