基于激光自混频效应的大气颗粒物在线监测技术

Particulate matter is one of the most important factors in the air pollution. Monitoring the particulate matter in air is an important topic in the area of measurement of multi-phase flow and it has attracted concerns worldwide. Currently, monitoring systems used are mainly based on the tapered element oscillating microbalance (TEOM), the beta attenuation monitor (BAM), light scattering such as the optical particle counter and etc. However, the TEOM and BAM are usually unable to work properly under the conditions of high temperature and high relative humidity. Techniques based on light scattering are still suffering from the disadvantages of low sensitivity due to the low level of signal, low measurement accuracy, low stability and etc. Therefore, the project proposes a new method for the real-time, on-line measurement of the ambient particulate matter on the basis of laser self-mixing technique. The scattered light is fed into the cavity of the laser wherein the interference between the scattered light and the internal field takes place and hence the signal is amplified so that the signal sensitivity is improved. With the compact LDPD module and its autocollimation, the measurement zone can be defined automatically. The measurement arrangement is very simple and more stable. The investigation will focus on the Lang-Kobayashi rate equations in the cases of both weak and strong feedback, the signal processing of the scattered light of particles illuminated by a focussed Gaussian beam and the relevant optimization. The research will lead to a new realtime and online measurement method which can be used in the monitoring of the air pollution and the clean space. Due to the distinctive design of the optical arrangement, it may also apply to the in-situ measurement of particles suspended in liquid.

大气颗粒物是最重要的大气污染物之一，大气颗粒物的监测是两相流测试技术的重要研究课题，也是当今国际社会的关注热点。对大气颗粒物的监测技术主要有微量振荡天平法、β射线法和光散射法等。微量振荡天平法和β射线法在高温潮湿地区适应性差、故障率高，光散射法在探测效率、测量准确度和系统稳定性等方面存在不足。本申请项目提出一种基于激光自混频效应的大气颗粒物在线监测方案：将颗粒的散射光注入到激光器谐振腔，通过散射光与腔内激光的自混频放大效应提高信号监测灵敏度；采用LDPD模块及其自准直优势实现测量区的定义、系统的简化从而提高系统稳定性。项目研究涉及Lang-Kobayashi速率方程在弱注入和强注入情况下的物理模型、高斯光束照射下颗粒散射光信号处理及优化。项目研究成果可望形成一种新的在线实时监测技术用于大气颗粒物监测、工业洁净空间监测。此外，由于其独特的光学结构，还可应用于分散在液相中的颗粒物原位监测。

大气颗粒物是最重要的大气污染物之一，大气颗粒物的监测是两相流测试技术的重要研究课题，也是当今国际社会的关注热点。本项目旨在发展一种基于激光自混频效应的大气颗粒物在线监测方案：将颗粒的后向散射光注入到激光器谐振腔，通过散射光与腔内激光的自混频放大效应提高信号监测灵敏度；采用LDPD模块及其自准直优势实现测量区的定义、系统的简化从而提高系统稳定性。项目对相关的关键技术问题展开研究：(1)在理论上深入研究了圆形高斯光束和椭圆形高斯光束的散射理论，通过引进Bessel函数和改进型Bessel函数，简化了局域化近似计算方法，将广义米理论框架下的正交积分法二维积分和角谱展开法的二维积分方法简化为一维积分，从而使得有形光束散射的计算速度更快、效率更高、更稳定、结果更可靠；在此基础上，构建了高斯光束照射下球形颗粒的后向散射信号物理模型，分析了散射光信号与颗粒物性参数和入射光的关系；(2)搭建了后向散射光探测装置并采用标准颗粒进行实验验证。实测研究表明，单个颗粒流经测量区时散射光信号表现为高斯型脉冲，脉冲峰值与颗粒粒径存在对应关系，脉冲宽度与颗粒粒径、颗粒流速以及光束束腰宽度有关。单位时间内散射光信号脉冲数与颗粒浓度成正比。(3)研究了从散射光信号中提取颗粒粒径分布信息的反演算法，提出了矢量相似度算法、发展了B-Spline基函数法，改进了非负约束的Tikhonov正则化算法和多参数Tikhonov正则化算法。项目研究为大气颗粒物在线实时监测仪的研发提供了理论基础和实验依据。项目研究成果可望形成一种新的在线实时监测技术用于大气颗粒物监测、工业洁净空间监测。此外，由于其独特的光学结构，还可应用于分散在液相中的颗粒物原位监测。