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Description
We present a novel configuration of a light source and a detection scheme optimized for high-sensitivity dual-optical frequency comb gas absorption spectroscopy in the mid-infrared. Using our free-running wavelength-tunable single-cavity dual-comb optical parametric oscillator and our simple intra-cavity upconversion-based detection scheme, we demonstrate heterodyne measurements with a signal-to-noise ratio of 50 dB Hz^{1/2} and a figure of merit of 3.5x10^8 Hz^{1/2}. These results are enabled by a low-noise laser source, high-power per comb line, the usage of low-noise InGaAs-detectors, and a time-gating effect in the up-conversion process limiting the instantaneous shot-noise. In a 10-ms long proof-of-concept measurement, we detect 2 ppm of ambient methane over a 3-m path length.
