Patent ID: 7969576
Filing Date: 2011-06-28
Classification: G01J,G01N

Abstract:
1. A method for optically sensing a gas medium based on Wavelength Modulation Spectroscopy, comprising: modulating a laser wavelength of a tunable laser at a modulation frequency to produce a wavelength-modulated laser beam with a laser frequency range including an absorption band of molecules of a molecular species in the gas medium; directing the wavelength-modulated laser beam that transmits through the gas medium; measuring a transmission of the wavelength-modulated laser beam through the gas medium to obtain measurements of at least one signal at a harmonic frequency of the modulation frequency at different modulation depths in modulating the laser wavelength; processing the measurements of the at least one signal at the harmonic frequency of the modulation frequency at different modulation depths to obtain a total broadening of absorption spectrum of the molecular species in the gas medium, wherein the at least one signal comprises a first signal at a second harmonic frequency of the modulation frequency, and wherein measuring the transmission of the wavelength-modulated laser beam through the gas medium comprises obtaining measurements of a second signal at a fourth harmonic frequency of the modulation frequency at different modulation depths in modulating the laser wavelength; and processing the measurements of the second signal to obtain additional information on the gas medium.