Fig. 1. (a) Line strength at different temperatures for each line. (b) Line strength ratio and relative sensitivity of target lines at different temperatures.

Fig. 2. Experimental setup. EDFA: erbium-doped optical fiber amplifier; HNLF: highly nonlinear fiber; BPF: bandpass filter; CP: coupler; ACS: asynchronous clock signal; PES: phase error signal; FAC: fast acquisition card; CLK: clock; CH: signal input channel; M: mixer.

Fig. 3. Spectra of two combs from the fiber oscillator (gray solid line), broadening spectra after the highly nonlinear fibers (blue dotted line), and filtered spectra (red area) for (a) comb and (b) comb B respectively.

Fig. 4. (a) Dual-comb interferograms of a single measurement (black) and 3×103-fold time-domain averaging (pink). (b) Comparison of the absorption line of water vapor at 296 K with the HITRAN database.

Fig. 5. Multiple-peak Voigt fit (solid line) to the measured spectral absorbance (dotted line) at different temperatures. The corresponding relative residuals normalized to the peak value of the respective fitting curve are shown on the top panel with a range from −10% to 10%.