Abstract
In this paper, a multi-frequency wavelength modulation spectroscopy (WMS) method for tunable diode laser absorption spectroscopy (TDLAS) tomography was proposed. Multiple wavelengths modulated at different frequencies were used to extract the absorption spectrums in parallel along various laser paths. For a five-view fan-beam TDLAS sensor, the wavelength of incident laser was respectively modulated by the high-frequency sinusoidal signal at six different frequencies to separate absorption spectrums at different angles and different wavelengths and then distributions of temperature and water vapor's molecules concentration can be reconstructed. The framerate of the proposed multi-frequency WMS method for image reconstruction is ten times faster than single-frequency WMS method with cascade laser scanning. Numerical simulations were conducted to verify the effectiveness of the proposed method with two absorption spectra of water molecule, $\nu$ 1=7185 cm−1 and $\nu$ 2=7444 cm−1. Three different distributions of temperature and water vapor's molecules concentration were fabricated and reconstructed.
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