An efficient approximation for a wavelength-modulated 2nd harmonic lineshape from a Voigt absorption profile

In this paper we report on an efficient approximation for the reconstruction and fitting of 2nd harmonic, wavelength-modulated, absorption spectra from Voigt profiles. The model consists in a proper combination of results recently obtained by other authors, concerning on one hand, Fourier analysis of signals resulting from wavelength modulation spectroscopy and, on the other hand, an empirical analytical approximation to the Voigt lineshape. The fitting algorithm was tested both on simulated and real spectra, corresponding to ammonia rovibrational transitions around 2-μm wavelength. In the case of real spectra, a standard deviation for the normalized residuals at a level of ∼0.2% was found. The accuracy in the reproduction of peak intensities was comparable with that provided by a more complex model, previously developed by other authors.