Tunable dual-comb spectrometer for mid-infrared trace gas analysis from 3 to 4.7 μm

Abstract

Dual-frequency comb spectroscopy has emerged as a disruptive technique for measuring wide-spanning spectra with high resolution, yielding a particularly powerful technique for sensitive multi-component gas analysis. We present a spectrometer system based on dual electro-optical combs with subsequent conversion to the mid-infrared via tunable difference frequency generation, operating in the range from 3 to 4.7 $\hat{I}¼$m. The simultaneously recorded bandwidth is up to 454(1) GHz and a signal-to-noise ratio of 7.3(2) x 10${}^2$ Hz${}^{-1/2}$ can be reached. The conversion preserves the coherence of the dual-comb within 3 s measurement time. Concentration measurements of 5 ppm methane at 3.3 $\hat{I}¼$m, 100 ppm nitrous oxide at 3.9 $\hat{I}¼$m and a mixture of 15 ppm carbon monoxide and 5 % carbon dioxide at 4.5 $\hat{I}¼$m are presented with a relative precision of 1.4 % in average after 2 s measurement time. The noise-equivalent absorbance is determined to be less than 4.6(2) x 10${}^{-3}$ Hz${}^{-1/2}$.

12 pages, 6 figures