Design and implementation of a Fourier transform spectrometer with a broadband optical frequency comb

We report a home-built femtosecond laser frequency comb-based continuous scanning Fourier transform spectrometer (FC-FTS) for the spectroscopy of gas phase molecules at a spectral resolution of 0.06 cm-1 working in a tunable wavelength range from 2900 nm (3450 cm-1) to 4600 nm (2174 cm-1). The FC-FTS employs a homemade broadband mid-infrared femtosecond laser frequency comb (FC) and a narrow linewidth He:Ne laser as a reference source for sampling the dependence of the interferogram signals on the optical path differences (OPDs). Both real-time correction and OPD resampling are achieved via precise zero-crossing analysis of the He:Ne reference laser interference signal, processed by customer-developed software to effectively compensate for mechanical perturbations. Software-based bandpass filtering, autobalancing, and etalon suppression of the OPD interferogram can improve the signal-to-noise ratio of the molecular spectra by nearly two orders of magnitude in a single sampling experiment. Both hardware and software frameworks have been presented, respectively. We also report the absorption spectra of four molecular species (acetylene, carbonyl sulfide, methane, and water) using the FC-FTS system, validating its utility for molecular fingerprinting. The concentration of each molecular species has been determined through spectral fitting analysis, wherein the experimentally measured absorption spectra are matched to the simulated spectra derived from the high-resolution transmission molecular absorption database. The developed diagnostic system achieves high-resolution, multispecies quantification, enabling precise identification of trace components in complex molecular systems.