Tunable Diode Laser Absorption Spectroscopy (TDLAS) applies optical method to realize fast and non-contact detection. This technology has the advantages of high resolution and high sensibility, and been widely employed in atmosphere environment detection in recent years. This paper mainly introduces how TDLAS is applied to detect the vehicle exhaust, to determine the content of CO, CO2, NO and alkanes etc. Firstly, the principle of TDLAS is Lambert-Beer's law. It is based on the specific spectral "fingerprint" characteristics of different gases to detect the gas composition. In the same time, the light intensity is attenuated by molecular absorption, which is used to accurately analyze the density of gas. There are two ways to achieve. One is direct-absorption way, whose configuration and signal processing are simple, results have no need to be demarcated. The other is wavelength-modulation way, which has high resolution and low threshold. The selection of absorption spectral line needs not only to adapt the central wavelength of laser and responding wavelength of detector, but also to avoid the crossed spectral line of different gas to improve the precision of detection. Secondly, TDLAS system includes three parts, which are signal generation, signal detection and signal processing. Finally, TDLAS is compared with other spectral detection technologies in the aspect of sensitivity, character of working, applicable kinds of gas, in order to highlight the application scope of each technology.
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