Analysis of periodic temporal changes in the spectral signature of IR sources by modeling of spectral artifacts in FTIR systems

Periodic fluctuations in the incoming spectrum to a Fourier-transform infrared (FTIR) spectrometer often result in spectral artifacts that can compromise quantitative measurements. This study presents a novel method that relaxes the conventional assumption of uniform fluctuations across all frequencies, by modeling the radiance fluctuations with a Fourier series expansion with wavenumber-dependent coefficients. By limiting the incoming spectral bandwidth with an interference filter, it is possible to retrieve the artifact-free average spectrum and to obtain the temporal evolution of the incident radiance. Experimental validation was conducted with transmittance measurements on a methane gas sample whose column density was periodically modulated. This method expands FTIR capabilities, particularly for applications involving fluctuating gases, and enhances the potential for time-resolved analysis in complex environments.