An accurate algorithm for calibration-free wavelength modulation spectroscopy based on even-order harmonics

This paper proposes an accurate algorithm to implement calibration-free wavelength modulation spectroscopy based on even-order harmonics. The proposed algorithm, analytically deduced from a much more accurate Voigt function model, enabling not only speedy measurement down to milliseconds, but also a general suitability for various degrees of line-shape broadening. The proposed method is validated by condition-controlled experiment, indicating calculation of gas temperature with the relative error less than 2.4% in the experiments.