Fourier-filtered, fast wavelength-scanned cavity ring-down spectroscopy

This paper presents accurate measurements of molecular absorption spectra using wavelength-scanned cavity ring-down spectroscopy (CRDS) based on Fourier transforms. The characteristic frequencies of the periodic ring-down time are extracted after the Fourier transform to recover the absorbance and significantly reduce the noise, especially the troublesome wavelength fluctuations. This method is simpler and has lower noise than conventional swept-cavity continuous-wave CRDS (S-CRDS). The smaller fitting residuals of the measured C O 2 ( 6526.374 c m − 1 ) and CO ( 6371.299 c m − 1 ) spectra show that the laser wavelength fluctuation effects are effectively reduced and the spectral SNR is improved. The measured N 2 and Ar perturbed spectral parameters for C O 2 are consistent with the S-CRDS method results but with smaller uncertainties.