空气中O2和N2摩尔分数的拉曼散射多通道测量

开发了一套基于激光拉曼散射的多通道气体光学检测系统,应用于空气中主要组分的摩尔分数定量测量.针对性的设计了532 nm激光脉冲展宽器,能有效地避免脉冲激光在高能量状态下造成气体裂解、石英玻璃损伤等现象的发生,提高了气体拉曼散射的信噪比.在实验室环境压力和温度下,对气体样池内空气进行了长66 mm×直径1 mm激发区域同步10通道(每通道长约6.6 mm)的拉曼散射实验.得到了各通道下氧气(O2)和氮气(N2)的拉曼光谱和摩尔分数,及O2相对于N2的相对响应因子RO2.完成了26次重复性实验,每次为200个激光脉冲激发自发拉曼光谱的累加.结果表明,各通道间计算的平均的氧摩尔分数x-O2和相对于氮气的相对响应因子-RO2的标准偏差分别为0.015和0.024,但它们的平均值与10通道合并方式下的实验结果完全相同,准确率达98%,完全满足实时地并具有时空分辨力的定量测量混合气体摩尔分数的要求.该系统可满足于各种动态燃烧过程的光谱检测与分析.

Laser Spontaneous Raman Scattering Based on Multi-Channel Measurement of Mole Fraction of Air

Based on the laser Spontaneous Raman Scattering (SRS)technique,a multi-channel optical diagnos-tic system is developed for quantitative measurement of mole fraction of gas.A laser pulse stretcher is designed for the 532 nm green laser to efficiently avoid any unwanted phenomena including gas cracking and quartz glass damage due to the impact of high-energy of pulsed laser.The system can also be used to enhance the signal-to-noise ratio of gas Raman scattering spectrum.Under a standard atmospheric temperature and pressure,Raman scattering measurements are carried out in an air excitation zone within a gas cell.The length and the diameter of the cylindrical excitation zone are 66 and 1 mm respectively.Raman spectroscopy and mole fraction of O2 and N2 within each channel are obtained from the tests,together with the relative response factor of O2 to N2 , the RO2 .In total,26 repeated experiments are conducted;and all of them are deduced from an accumulated spectrum of 200 laser shots.It shows that the standard deviations between the results of each channel in terms of the averaged mole fractions of O2 ,x-O2 and the averaged relative response factor of O2/N2 ,-RO2 are 0.015 and 0.024,respectively.However,the channel-averaged value of these parameters is exactly the same as the result obtained with a merged-channel-mode.The accuracy of the measurement is 98%,indicating that this system can fully meet the requirements of real time quantitative measurement for mole fraction of gas mixture with providing spatial and temporal resolution.The present system satisfies the spectral measurement and a-nalysis of various dynamic combustion processes.