Absorption spectrum technology-based dual frequency wavelength modulation method

Abstract

The invention discloses an absorption spectrum technology-based dual frequency wavelength modulation method. The method comprises the following steps: superposing another high frequency sinusoidal signal on a traditional wavelength modulation signal, establishing a dual frequency wavelength modulated Fourier analysis model for a laser excitation manner, theoretically deriving every subharmonic expression, researching the influences of different modulation parameters on the harmonic signal, and determining best modulation parameters through a global optimization algorithm; and determining the function expression of a dual frequency wavelength modulation frequency response relation. Compared with conventional single frequency wavelength modulation methods, the measurement method provided by the invention has the advantages of high signal-to-noise ratio, high stability of a measurement result , easiness in judgment of the harmonic peak value under a weak absorption condition, large application potential, changing of the injection current excitation manner of a laser device, and low hardware cost requirements, and can be applied to a multi-reflection cell and other systems to further reduce the detection limit of the gas concentration.

Description

technical field [0001] The invention relates to a dual-frequency wavelength modulation method based on absorption spectroscopy technology, which is used for gas concentration measurement and belongs to the technical field of laser absorption spectroscopy. Background technique [0002] Tunable Diode Laser Absorption Spectroscopy (TDLAS) makes full use of the narrow linewidth and tunable characteristics of distributed feedback lasers, and realizes the rapid scanning and measurement of a single absorption line of gas molecules, with a low detection limit , high sensitivity, fast response, non-invasive and other advantages, has been widely used in near-infrared band trace gas detection, environmental protection and pollution emission monitoring, combustion diagnosis of coal-fired boilers and aerospace engine detection. However, since the vibration-rotation bands of most molecules are located in the infrared spectrum region, and the absorption intensity of molecules in this band ...

AI Technical Summary

Problems solved by technology

FMS and WMS are mostly used for gas calibration and detection, and need to be calibrated in a known system, which is difficult to achieve in most environments

In addition, when the gas temperature, pressure and etalon effect (interference fringes generated by parallel planes) change, the measured gas parameters will bring great uncertainty, which is not suitable for the harsh measurement environment on site

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