High-sensitive carbon disulfide sensor using wavelength modulation spectroscopy in the mid-infrared fingerprint region

•A CS2 sensor with high-sensitive of detection limit 19.5ppb, corresponding absorbance as 3×10−5 for band spectrum was provided.•The optimized modulation index reasonably balanced the spectral discrimination and the SNR in WMS with band spectrum.•The optical fringes buried in the detected signal was distinguished and removed by EMD algorithm.•The robust and versatile method enabling WMS to band spectrum is instructive for VOCs detection. A sensitive carbon disulfide (CS2) sensor based on wavelength modulation spectroscopy (WMS) in the mid-infrared fingerprint region was reported. The strong band spectrum of carbon disulfide's combination band (ν1+ν3), near 2177.6cm−1, was used in the sensor. To enable WMS for wideband spectrum, a parameter of Spectral Discrimination (SD) was defined and used as a criterion for optimizing the modulation index, which was finally determined to be around 0.8 instead of 2.2 commonly used for an isolated line spectrum. And the second harmonic signal was processed with empirical mode decomposition (EMD) algorithm to distinguish and remove the optical fringes buried in the detected signal. The sensor performances were tested by implementing a set of CS2 concentration experiments. The results showed that the sensor response linearity was 0.999 and the relative measuring error was less than 1%. The sensitivity, i. e. 3σ detection limit, was as low as 60ppb with integration time of 240s with optical path length of 5m, corresponding to absorbance of 3×10−5. Overall, benefiting from strong fingerprint absorption and methods of applying WMS to wideband spectrum, the sensor is promising for both environmental and industrial CS2 detection.