Measurement Principles. An infrared laser such as a tunable diode laser (TDL) (e.g. those used in a Laser Diode Spectrometer (LDS)), or a quantum cascade laser (QCL) can emit coherent light in the near-infrared region or in the mid-infrared region respectively, where nitrogen compounds including NH3 have strong absorption. These laser optics give a pulsed-mode high resolution narrow band near-infrared or mid-infrared spectrum. Therefore, laser infrared analysers can reduce interference caused by the spectral overlap of co-existing components in engine exhaust gas.
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Sources: Agreement Concerning the Adoption of Harmonized Technical United Nations Regulations for Wheeled Vehicles, Agreement Concerning the Adoption of Harmonized Technical United Nations Regulations for Wheeled Vehicles, Agreement Concerning the Adoption of Harmonized Technical United Nations Regulations for Wheeled Vehicles