Telecom-grade fiber laser-based difference-frequency generation and ppb-level detection of benzene vapor in air around 3 μm

International audienceWe report on the development of a field deployable compact laser instrument tunable over ˜232 cm-1 from 3.16 to 3.41 μm (2932.5-3164.5 cm-1) for chemical species monitoring at the ppb-level. The laser instrument is based on widely tunable continuous-wave difference-frequency generation (DFG), pumped by two telecom-grade fiber lasers. DFG power of ˜0.3 mW near 3.3 μm with a spectral purity of ˜3.3 MHz was achieved by using moderate pumping powers: 408 mW at 1062 nm and 636 mW at 1570 nm. Spectroscopic performance of the developed DFG-based instrument was evaluated with direct absorption spectra of ethylene at 3.23 μm (˜3094.31 cm-1). Absorption spectra of vapor-phase benzene near 3.28 μm (˜3043.82 cm-1) were recorded with Doppler-limited resolution. Line intensities of the most intense absorption lines of the ν 12 band near 3043.8 cm-1 were determined to support development of sensitive mid-infrared trace gas detection of benzene vapor in the atmosphere. Detection of benzene vapor in air at different concentration levels has been performed for the first time using multi-pass cell enhanced direct absorption spectroscopy at ˜3.28 μm with a minimum detectable concentration of 50 ppb (1 σ)