Fig. 1. Schematic of a broadband MIR dual-comb spectrometer. fr: repetition rate; fceo: carrier-envelope offset frequency; EDFA: Er-doped fiber amplifier; HNLF: highly nonlinear fiber; SCG: supercontinuum generation; YDFA: Yb-doped fiber amplifier; DM: dichroic mirror; CPPLN WG: chirped periodically poled lithium niobate waveguide; MIR DFG: mid-infrared difference frequency generation; OFP: optical filter plate; BS: beam splitter; BPD: balanced photodiode.

Fig. 2. (a) Evolution of the signal spectra in the HNLF. (b) Evolution of the signal temporal profile in the HNLF. (c) Numerical simulation of the output SCG spectra at HNLF lengths of 2 cm (light gray line), 3 cm (red line), and 4 cm (dark gray line). (d) Experimental measurement of the output signal light supercontinuum spectral result. Measurement devices: Yokogawa AQ6370 (blue line) and Bristol 771B (orange line).

Fig. 3. Pump pulse spectra in the master (a) and slave (b) paths. Signal pulse spectra in the master (c) and slave (d) paths.

Fig. 4. (a) Calculated signal wavelength versus PPLN period at a 1064 nm pump wavelength, considering with (red line) and without waveguide dispersion (blue line). (b) Poling structure of the chirped PPLN waveguide, with (red line) and without waveguide dispersion (blue line). (c) Measured spectra of generated MIR combs in the master (red shadow) and slave (blue shadow) paths.

Fig. 5. Temporal dual-comb interferograms with time scales of 21 periods (a), a single period (b), and a partial period (c). (d) Converted dual-comb spectrum with a 200 s average time. (e)–(h) Typical mode-resolved comb lines in partial frequency windows.

Fig. 6. (a) Converted dual-comb absorption spectra at the MIR atmospheric windows. (b)–(i) Typical dual-comb absorption lines for multiple greenhouse gas molecules. (j) Evolution of the spectral average SNR as a function of the average time.