Broadband and flat-baseline dual-comb cavity mode dispersion spectroscopy using fiber-based frequency combs
We demonstrate broadband dual-comb cavity mode dispersion spectroscopy using mode-locked erbium-fiber frequency combs and a length-tunable optical cavity. The flat baseline and low-noise characteristics of cavity-mode-dispersion spectroscopy, combined with the broadband coverage of fiber frequency combs, provide highly precise spectral profiles that are difficult to obtain with conventional dual-comb spectroscopy. We measured the entire $\nu_1 + \nu_3$ band of acetylene in the $1.5~\mathrm{\mu m}$ region. The simultaneous fitting of multiple transitions agreed well with the measured spectra, yielding a relative standard deviation of 0.27 % for the retrieved acetylene pressure and a spectral fluctuation corresponding to an absorption coefficient of $1.4\times 10^{-6}~\mathrm{cm}^{-1}$. These results reveal the high precision achievable with the present method. Further sensitivity improvements are expected with a higher-finesse cavity.