Adaptive cavity-enhanced dual-comb spectroscopy

Resolution and bandwidth are critical for cavity-enhanced dual-comb spectroscopy（CE-DCS）. Here, we pioneer an adaptive approach in CE-DCS to improve the broadband as well as the resolution. Postcorrections to dualcomb interferograms adaptively compensate the relative phase jitters of the optical frequency combs and result in both a mode-resolved spectral resolution and a signal-to-noise ratio of 440:1 in 1 s. Meanwhile, an adaptive combcavity locking scheme exploits more than 90% of the comb modes, covering 340 cm;（10 THz） at 6450 cm;. For a single dual-comb interferogram, more than 40,000 comb teeth spaced by 250 MHz are measured in less than7.5 ms, contributing to a noise equivalent absorption per spectral element of 2 × 10;cm;·Hz;. This adaptive cavity-enhanced dual-comb spectroscopy technique provides an attractive spectroscopic tool that may be utilized in trace-gas sensing, breath and cancer analysis, and engine combustion diagnosis.