Mid-infrared optical frequency comb-based Fourier transform spectrometer for broadband molecular spectroscopy

Optical freciuency comb-based Fourier transform spectroscopy has the features of broad spectral bandwidth, high sensitivity, and multiplexed trace gas detection, which has valuable application potential in the fields of precision spectroscopy and trace gas detection. Here, we report the development of a mid-infrared Fourier transform spectrometer based on an optical frequency comb combined with a Herriott-type multipass cell. Using this instrument, the broadband absorption spectra of several important molecules, including methane, acetylene, water molecules and nitrous oxide, are measured by near real-time data acquisition in the 2800-3500 cm⁻¹ spectral region. The achieved minimum detectable absorption of the instrument is 4.4xl0⁻⁸ cm⁻¹·Hz^−1//2 per spectral element. Broadband spectra of H₂O are fitted using the Voigt profile multispectral fitting technique and the consistency of the concentration inversion is 1%. Our system also enables precise spectroscopic measurements, and it allows the determination of the spectral line positions and upper state constants of N₂O in the (0002)-(1000) band, with results in good agreement with those reported by Toth [Appl. Opt. 30, 5289 (1991)].