A dual-comb spectrometer for trace gas analysis in the mid-infrared

Abstract

A dual frequency comb spectrometer is realized by electro-optic modulation of a 1550 nm laser and subsequent conversion to the mid-infrared by difference-frequency generation (DFG). Using an optical parametric oscillator for the DFG the combs can be tuned from 3 μm to 4.7 μm with 440 comb modes covering 220 GHz (< 6 cm^-1). Trace gas detection of nitrous oxide, carbon dioxide and methane is demonstrated with a 7.2-m-multi-pass cell while a sufficiently low noise-equivalent absorbance is reached in already 1 s. The bandwidth normalized noise-equivalent-absorption coefficient is consistently below 2.8 × 10-6 Hz^-1/2 cm^-1 while the precision of the determined concentrations is better 2 % Hz^-1/2.