Sensitive multi-species trace gas sensor based on a high repetition rate mid-infrared supercontinuum source.

We present a multi-species trace gas sensor based on a high-repetition-rate mid-infrared supercontinuum source, in combination with a 30 m multipass absorption cell, and a scanning grating spectrometer. The output of the spectrometer is demodulated by a digital lock-in amplifier, referenced to the repetition rate of the supercontinuum source. This improved the detection sensitivity of the system by a factor 5, as compared to direct baseband operation. The spectrometer provides a spectral coverage of 950 cm (between 2.85-3.90 µm) with a resolution of 2.5 cm in 100 ms. It can achieve noise equivalent detection limits in the order of 100 ppbv Hz for various hydrocarbons, alcohols, and aldehydes.