大气气溶胶吸收特性的光纤式光热干涉测量技术研究

发布时间：2018-04-11 09:52

本文选题：大气气溶胶 + 吸收系数　；参考：《中国科学技术大学》2017年博士论文

【摘要】：大气气溶胶粒子的光吸收虽一般比较微弱,但对地球大气辐射收支平衡、激光大气传输等均具有重要影响。目前,大气气溶胶粒子吸收系数的精确测量越来越受到重视,已经成为一个研究热点与技术难点。光热干涉技术通过测量气溶胶粒子光吸收热扩散效应产生的折射率变化,实现了自然悬浮状态下气溶胶粒子吸收特性的直接获取,有效规避了粒子散射光的影响,同时干涉测量又具有极高探测灵敏度,因此光热干涉技术被认为是一种极具发展潜力的大气气溶胶粒子吸收系数测量手段。本文针对大气气溶胶吸收特性的光纤式光热干涉测量技术进行了深入研究,阐明了光热干涉技术测量原理,包括光热效应、光相位调制及光相位解调等,并根据实际大气气溶胶吸收特性测量需求,研制了一套光纤式光热干涉实验装置,完成了不同吸收特性样品的初步测量。本文主要研究结果及创新点如下:(1)利用气溶胶粒子吸收的光热效应,从热传导方程出发,建立了激励光加热气溶胶的"光-热-折射率-相位"转化过程的理论模型,构造了大气气溶胶粒子吸收系数与干涉仪输出相位差之间的直接联系。(2)提出了同步载波复原的方法,有效的消除了相位生成载波调制解调算法中干涉信号与混频信号的载波延迟问题;利用参考光路解决了光源直接频率调制导致的伴生调幅现象;完成了基于相位生成载波调制解调算法的光热干涉解调与控制软件的编写、优化与验证测试,具备了气溶胶吸收激励光能量生成诱导相位起伏的全过程在线研究能力。(3)设计并研制了一套可用于大气气溶胶吸收特性测量的光纤式光热干涉实验装置;采用特制光纤准直器与高反镜实现了共光路光纤式斐索干涉结构,仅通过普通单模光纤就消除了系统偏振衰落现象;结合一体化光热干涉腔,有效增强了装置的抗干扰能力,提升了光热耦合效率和探测灵敏度。(4)阐明了光纤式光热干涉实验装置的标定原理并利用二氧化氮标准气体对装置进行了标定;以含碳气溶胶作为待测样品,二氧化氮标准气体与高纯氮气作为对照样品,完成了气溶胶吸收特性的初步测量,所得实验结果均与理论分析结果相符,为大气气溶胶吸收特性的进一步研究奠定了技术基础。
[Abstract]:Although the light absorption of atmospheric aerosol particles is generally weak, it has an important effect on the balance of the earth's atmospheric radiation budget and laser atmospheric transmission.At present, more and more attention has been paid to the accurate measurement of atmospheric aerosol particle absorption coefficient, which has become a research hotspot and technical difficulty.By measuring the refractive index change of aerosol particle photoabsorption thermal diffusion effect, the photothermal interferometry can directly obtain the aerosol particle absorption characteristics in the natural suspension state, and effectively avoid the influence of particle scattering light.At the same time, the interferometry has high detection sensitivity, so the photothermal interferometry is considered as a promising method for measuring the absorption coefficient of aerosol particles in the atmosphere.In this paper, the optical fiber photothermal interferometry for atmospheric aerosol absorption is studied, and the principle of photothermal interferometry is expounded, including photothermal effect, optical phase modulation and optical phase demodulation.According to the requirement of the measurement of atmospheric aerosol absorption characteristics, a set of optical fiber photothermal interference experimental device has been developed, and the preliminary measurement of the samples with different absorption characteristics has been completed.The main results and innovations of this paper are as follows: (1) based on the photothermal effect of aerosol particle absorption, a theoretical model of photothermal refractive index phase transformation of aerosol excited by photothermal heating is established from the heat conduction equation.The direct relation between the atmospheric aerosol particle absorption coefficient and the interferometer output phase difference is constructed.The problem of carrier delay between interference signal and mixed signal in phase-generated carrier modulation and demodulation algorithm is effectively eliminated, and the associated amplitude modulation phenomenon caused by direct frequency modulation of light source is solved by reference light path.The software of photothermal interference demodulation and control based on phase-generated carrier modulation and demodulation algorithm is written, optimized and validated.An optical fiber photothermal interference experimental device is designed and developed to measure the absorption characteristics of aerosol.Using special fiber collimator and high mirror, the common optical path fiber-optic Fieso interference structure is realized. The polarization fading phenomenon of the system is eliminated only by ordinary single-mode fiber, and the anti-interference ability of the device is effectively enhanced by combining the integrated photothermal interference cavity.The calibration principle of the optical fiber photothermal interference experimental device is clarified, and the calibration of the device is carried out by using nitrogen dioxide standard gas, and the carbon-containing aerosol is used as the sample to be measured.Nitrogen dioxide standard gas and high purity nitrogen were used as control samples to measure the absorption characteristics of aerosol. The experimental results were in agreement with the theoretical analysis results, which laid a technical foundation for the further study of the absorption characteristics of atmospheric aerosols.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X513;O439

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