【作者】 王会波；

【导师】 李志全；

【作者基本信息】 燕山大学 ， 检测技术与自动化装置， 2010， 博士

【摘要】 气体浓度测量和组分分析是一项重大的科学研究课题。因为随着石油、化工、煤炭、航天以及核能等工业的迅速发展的同时,产生了不同程度的有毒有害、污染环境的气体。这些气体虽然浓度很低,但和人类的健康、环境保护及超精密加工息息相关。多年来,各国学者对这一课题进行了大量的理论与实验研究,取得一些有价值的研究成果,并获得了重大的社会效益和经济效益。但在超低浓度气体的高灵敏度、高精度在线测量和组分分析中就难以胜任了。随着光谱学、化学分析及材料学等理论的发展和相互交叉,以及激光技术和新材料无源器件制作技术的快速发展,给解决这一问题提供了契机,出现了光腔衰荡、薄膜吸收和基于非线性的激光器调制与解调技术的新的测量方法及其理论。本文采用光纤环路光腔衰荡法对气体浓度测量进行了理论与实验研究,具体内容包括:对气体分子的近红外选择性吸收理论作了详细论述,分析了气体分子的运动形式及光谱,基频泛频和组合频率的光谱特性,给出气体吸收测量的理论依据,确定了多种气体的吸收谱线。介绍了光腔衰荡光谱技术进行气体浓度测量的基本理论,分析了气体谐波检测原理和光腔衰荡光谱原理,并对测量的特性参数作了理论分析。从耦合波理论出发,对测量系统的主要元件DFB-LD进行了深入研究,理论分析了DFB-LD的耦合方程,给出耦合波方程解,并对其空间烧孔效应进行了抑制。论述了DFB-LD的动态特性、张弛振荡机制及增益开关理论,并利用光纤光栅滤波器消除DFB-LD频率啁啾。构建基于光纤环路光腔循环衰荡法的气体浓度测量系统,建立了气体浓度测量数学模型,分析了气体谐振腔的特性与腔增强。设计了增益可调的掺铒光纤放大器,并理论分析了基于遗传算法与光子晶体器件的掺铒光纤放大器的平坦化方法,建立了掺铒光纤放大器增益平坦数学模型,并进行了相关仿真实验,整体的平坦效果明显,增益起伏大约为2dB左右。分析了基于气体吸收谱线法的差频激光器实验系统和方法,建立了其分析数学模型。对测量系统中由大功率固定波长的激光器Nd:YAG和可调谐二极管激光器TDL在PPLN晶体中差分,调制成宽范围的可调谐激光器采用PDH技术进行了激光稳频理论分析。针对气体浓度测量系统进行了相关实验与分析。实验主要包括可调谐激光器稳频实验;增益可调掺铒光纤放大器实验;可调光衰减器实验及气体浓度测量实验。通过分析得出了七种特定峰值波长的光分别在给定浓度七种气体中的衰荡时间,比较了不同浓度的同种气体对光的吸收特性,研究了光的衰荡时间、光的环路损耗与气体对光的吸收系数和气体浓度的关系。更多还原

【Abstract】 It is a great scientific research that the concentration measurement and component analysis of trace gas. The poisonous, harmful and contaminative gas from the petroleum, chemical, coal, space flight and nuclear energy industry is closely linked with human health, environmental protection and ultra-precision machining, although their concentrations are faint. Scientists have obtained many research achievement and acquired social and economic benefits after made a lot of theoretical and experimental studies on this subject for many years. But it is still ineffectual to on-line concentration measurement and component analysis of high sensitivity and precision of trace gas. Following the developing and crossover of spectroscopy, chemistry and material science, and the progress of laser and passive component fabrication technique, it provides an opportunity for solving the problem, and appeared many new technology, such as cavity ring-down, film absorption, and new measurement method based on nonlinear laser modulation and demodulation have come true. In this thesis, theoretic and experimental research have been made on gas concentration measurement used fiber loop cavity ring-down method, with the specific works as follows:The selective absorption theory of gas molecule in near infrared was detailed described; Movement form and spectrum of gas molecule, as well as spectrum characteristic of fundamental, fundamental frequency and combined frequency were analyzed; Theoretic basis of gas absorption measurement was provided; Various gas absorption spectrum was confirmed. Secondly, basic theories of cavity ring-down spectroscopy theory was described; Harmonic detection and cavity ring-down, hence, characteristic parameters were analyzed theoretically. Thirdly, according to coupled wave theory, the main component, DFB-LD, of the system was researched further. Theoretic analysis of coupled wave equation and it’s solution were discussed, and the spatial hole burning effect was suppressed. Finally, dynamic characteristics, relaxation oscillation mechanism, and gain-switched theory of DFB-LD were discussed, and the frequency chirp of DFB-LD was eliminated by fiber grating filter. Gas concentration measurement system based on fiber loop cavity ring-down was design, and mathematical model of which was established, besides, the characteristic of resonant cavity and cavity enhancement were analyzed. Secondly, variable gain erbium doped fiber amplifier was proposed, Flattening methods of EDFA based on photonic crystal and genetic algorithms were presented, and the mathematical model of which were given. According to the simulation, which gives evidence of flatness, the gain fluctuation is about 2 dB. Thirdly, experimental system of difference frequency laser based on absorption spectrum were analyzed, and mathematical model of which was established. In the system, difference frequency generation occurred in the PPLN crystal when Nd:YAG of high-power laser with fixed wavelength and tunable diode laser(TDL) operated, so we obtain a wide-range tunable laser, including PPLN crystal, PPLN crystal and TDL. Finally, PDH was used to steady frequency of the wide-range tunable laser.Related experimental study of the system including tunable laser frequency stable, variable gain erbium doped fiber amplifier, variable optical attenuator and gas concentration measurement. Seven different ring-down time of fixed peak wavelength laser measured from different gas cells were obtained, and the absorption characteristics of the same gas with different concentration were compared, finally, the relationship of ring-down time, loop loss, absorption coefficient and gas concentration were given.更多还原