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

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 2177.6 cm−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 60 ppb with integration time of 240 s with optical path length of 5 m, 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.