Research On CARS Spectra Of Gas Molecule In Combustion

The coherent anti-Stokes Raman spectra (CARS) of gas are investigated in this paper. Firstly, by using the Maxwell equations in the medium and the semiclassical theory of the interaction between electromagnetic wave and substance, the semiclassical theory of CARS is described on the basis of density matrix of quantized particles and Schr?dinger equation. Expressions of the nonlinear electric susceptibility of the third order and the CARS intensity in gas medium are deduced. The CARS spectra of nitrogen and carbon monoxide are calculated, the effect of laser linewidth of pump and stokes on the CARS spectra is discussed, and the relation of the CARS spectra with concentration, temperature is investigated. Then, the molecular structure, the vibrational-rotational energy level and the CARS theory of water and carbon dioxide is given. The CARS spectra of water and carbon dioxide are calculated, the relation of the CARS spectra with temperature is analyzed. Finally, based on the resonant frequency of molecule and the linewidth of dye laser, the multiplex CARS spectra of a mixture of nitrogen, carbon monoxide and hydrogen, when illuminated by a dye laser and a pump laser, are calculated, and also those of a mixture of carbon dioxide and hydrogen. The relation of the multiplex CARS spectra with temperature, multiplex species concentration is analyzed. It is indicated from the results that both the temperature of the combustion and the concentration of multiplex species can be obtained with multiplex CARS simultaneously.