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High-precision sensing of chemical warfare simulants using mid-infrared spectroscopy

We show mid-infrared detection of chemical warfare simulants using rapidly tuned and broadband mid-infrared laser spectroscopy suite of chemical species with disparate absorption cross-sections. Sarin gas is one of the most lethal chemical weapons with significant impacts at trace concentrations as low as 64 ppbv within a very short exposure time. In this research, we develop theoretical models to design a mid-infrared (8-11 μm) detection system for high-precision sensing of trace chemical-warfare agents. The models are based on absorption cross-sections and theoretical estimation of chemicals using direct-absorption spectroscopy. Due to the extremely hazardous nature of Sarin, Triethyl Phosphate (TEP), which has a very similar structure to Sarin, was chosen as a proxy chemical. TEP is a standard simulant for organophosphate nerve agents like Sarin. We use a combination of direct absorption spectroscopy and wavelength modulation spectroscopy to resolve and detect line-broadened transitions of TEP. Thus, by analyzing the regression slope of the theoretical absorption cross-section and experimental absorbance, TEP concentration can be estimated in a congested molecular spectrum. The absorption cross-section was modeled using Doppler and Voigt profiles.