连续波环形腔震衰减光谱测量技术研究

发布时间：2017-12-27 08:46

  本文关键词：连续波环形腔震衰减光谱测量技术研究　出处：《中国科学院研究生院(长春光学精密机械与物理研究所)》2016年博士论文　论文类型：学位论文

  更多相关文章： 光学测量 激光吸收光谱技术 腔衰荡光谱测量 光学无源谐振腔 模式匹配 痕量气体浓度 超高反射率测量

【摘要】：光学谐振腔的光腔损耗主要分为以下几个方面,包括:衍射损耗、几何偏折损耗、反射不完全损耗、腔内介质的吸收损耗等。其中,衍射损耗包括因腔镜大小产生的衍射损耗以及因腔镜失调产生的附加衍射损耗;光线在腔内往返传播时,可能从腔的侧面偏折出去,这种损耗为几何偏折损耗,稳定腔内傍轴光线的几何损耗应为零;利用腔镜的反射不完全损耗的特点,同样通过探测谐振腔出射光强的衰减,得到腔镜反射率的绝对值,该特点目前已得到广泛关注,将成为腔镜超高反射率值的测量的唯一手段。在超高反射率测量技术领域中具有绝对优势;对由于腔内介质存在的吸收损耗的这一特点,以及对于不同气体“指纹”式的吸收谱线特性,根据朗伯比尔定律,通过测量谐振腔出射光强的变化来获得腔内待测气体浓度值,相关的技术包括腔增强光谱技术和腔衰荡光谱技术等。其中,腔震衰减光谱仪(CRDS,Cavity Ring-Down Spectrometer)是近年痕量气体分析仪器技术发展突破的标志。CRDS提供现有其它测试方法不可比拟的高性能比、适用苛刻现场应用条件的通用气体检测手段。在此,本文根据国内外的研究状况,以连续波环形腔衰荡光谱技术为重点,就与该技术密切相关的重大问题,包括环形腔结构特性、光束特性、激光器与谐振腔频率匹配、模式匹配、光轴对准、激光带宽特性以及扫描速度等问题进行了深入的研究,在此基础上建立了完整的光谱测量系统,并进行了大量的实验应用研究。并在此基础上对影响测量精度的一系列因素进行了深入研究。本文的主要内容和得到的结论可以概括如下:(1)对由两平面镜一球面镜构成的高品质无源腔的基于腔衰荡光谱测量技术中若干问题进行了研究,具体包括:首先,对三角形环形腔的光束特性进行了全面的分析,得到了腔内循环光的光束特性、频率特性以及偏振特性,为环形腔的应用打下了坚实的理论基础,为后续的测量系统的设计提供了良好的理论指导;其次,为了降低高斯光束与谐振腔耦合过程中,失调量和失配量对基于无源谐振腔测量技术精度的影响,采用高斯光束变换规律、模式耦合有关理论以及光束传播坐标变换等相关理论,就失调量和失配量对基模耦合效率的影响分别进行分析和模拟,并据此给出了一般情况下两个参考量同时存在时基模耦合效率的表达式;再次,从光束传输坐标变换的角度,分析了由多个平面镜所构成的谐振腔的共轭光轴存在条件,得出了奇数平面镜谐振腔仅当平面镜间具有高精度的相同垂直度时才存在闭合光轴,而偶数平面镜谐振腔总是存在闭合光轴的结论,并给出了腔共轭轴随腔镜方向失调而产生的角度变化关系。给出了谐振腔的设计参数以及依据。具体分析了由两个平面镜和一个球面镜构成的三角形环形谐振腔的闭合共轭光轴存在的问题,结果表明,当不同的镜子出现角度偏差时,腔内仍然存在闭合的共轭光轴,并给出了对应的腔轴变化以及新谐振面的位置及方向,由此说明由于球面镜的加入降低了谐振腔共轭轴存在性对平面镜间高精度平行度的要求,为基于高品质光学无源腔的光谱测量技术的高精度装调工作提供了理论指导;最后,本文没有从频率匹配的角度来考虑入射光的频率特性,因为简单的频率匹配不能更好的为入射激光的频率特性提出更好的限制性分析,为了更便于后续对激光器选型的参数确定,将从光学叠加原理,分别从时域和频域两个角度进行分析,给出了腔内光干涉过程,更好的为分析腔内光场特性提供了理论依据,以便更为方便对可能遇见的问题进行理论分析。(2)在充分的理论分析的基础上建立了连续波环形腔衰荡光谱技术测量方案。针对环形腔的理论分析结果,对连续波腔衰荡光谱系统的整体测量系统设计、控制系统设计、电路设计以及软硬件的实现进行了介绍。本文设计的系统具有以下的优点和创新,其中,以分布反馈式激光器(dfb)为光源,利用其温度、电流调谐特性实现激光波长的调谐从而实现“关断”,省略了与光开关的相关器件;测量系统以三角形环形腔作为谐振腔,减少了直接返回到激光器的光学面,省去了光隔离器;控制系统中采用高精度的波长计完成激光器频率的调节和锁定,在保证精度的前提下,省略了常用的基于相位调制锁定光学谐振腔所用的一系列激光器与谐振腔的锁定装置。在建立的测量系统基础上对相关设计参数进行了确定,并对测量系统中的各个器件进行性能测试,较为主要的结果为激光器的调谐关断时间为2μs内;pzt腔长调节范围为2.5nm,调整频率为1khz;波长计在波长为1000nm时其绝对精度可达±0.2pm,可满足高精度激光波长标定的要求,以上指标满足测量系统的理论要求。(3)对调腔式连续波环形腔衰荡光谱系统的特点及搭建实现进行了深入研究。以所述的理论为基础,在考虑光源光谱线宽的情况下,就光源光谱线宽的特性提出两种装调校准方案:基于法布里伯罗干涉仪法和基于多维象限探测器探测谐振腔出射光的调节回路,搭建了调腔式环形腔衰荡光谱系统,特点是该系统具有光轴校准的闭合控制能力。对所设计的谐振腔在相关光学软件上进行模拟分析,得到其衍射损耗与腔镜位置对应的变化关系;得到了腔出射光斑特性与腔长失调量之间的对应关系;得到了腔镜大小的限制以及其基膜模式分布特性,为谐振腔的装调提供了指导。更主要的是针对软件中不能给出的谐振腔的腔轴位置的问题进行了补充分析,得到了谐振腔镜角度失调对腔内闭合光轴的位置的影响,并进行了理论研究和数值模拟,得到了腔轴的位置变化与入射光的方向位置变化关系,并进行了初步的实验研究,验证了三角形环形腔腔参数设计的合理性,降低了三角形环形腔的装调难度。(4)对连续光波环形腔衰荡光谱技术影响探测精度的误差因素进行了初步研究。这些因素包括对激光器调谐扫描速度等问题进行了系统的分析,为了更方便描述激光器扫描速度的限制,在此引入了两个参数,扫描速度参数??c a v c a v??W?v?和带宽参数κ,并对腔出射光谱与?的数值模拟,得到了当?1时,腔衰荡光谱更接近单e指数衰减;对激光器带宽特性对测量的影响,得到了????时,腔出射线型中尖峰特性平稳,使得衰荡线型更趋于光滑的单e指数衰减;主要分析了压强对气体吸收特性的影响,以H2S气体为例,给出了如何确定目标气体的“无干扰”波段以及最佳操作压力的确定方法,为气体的探测最佳参数的确定提供了参考。(5)对腔体长~200 mm、总腔长~410mm环形腔衰荡光谱系统进行了实验研究,搭建了连续波激光器环形腔衰荡光谱测量系统。鉴于腔衰荡光谱技术的应用均是建立在对腔损耗值进行精确测量的基础上,本文将该测量系统应用于常温常压,无“干扰气体”吸收的反射镜超高反射率的测量上。利用高纯氮气对空腔进行反复冲洗,消除干扰气体的吸收光谱的影响得到反射镜的反射率更精确的测量值,最后确定反射镜的反射率在6046.972cm-1频率处的反射率精确值。此外,还对该系统在痕量气体浓度探测领域的应用进行了研究,并对影响测量精度的因素进行了详细分析。
[Abstract]:The optical cavity loss of optical resonator is mainly divided into the following aspects, including diffraction loss, geometric deflection loss, incomplete reflection loss, and absorption loss of cavity medium. Among them, the diffraction loss including the diffraction loss caused by mirror size and due to misalignment of cavity mirrors generated additional diffraction loss in the cavity; the light travels, probably from the cavity side out deflection, the loss of geometric deflection losses, the cavity loss near the geometric axis light consumption should be zero; the mirror reflection incomplete loss of the same through the detection of resonant cavity light attenuation, the absolute value of the reflectivity obtained, the characteristics of the present have been widely concerned, will become the only means to measure the value of the ultra high reflectivity mirror. Has the absolute advantage in high reflectivity measurement technology in the field of; because of the characteristics of the absorption medium in the cavity, and the absorption spectrum characteristics of different gas "fingerprint", according to Longbow Bill's law, to obtain the measured gas concentration cavity by measuring the resonant cavity light intensity changes, related technology including the cavity enhanced spectroscopy and cavity ringdown spectroscopy etc.. Among them, CRDS (Cavity Ring-Down Spectrometer) is a symbol of the breakthrough of the development of trace gas analysis instruments in recent years. CRDS provides an unparalleled high performance ratio and a general gas detection method for harsh field application conditions that are incomparable with other existing testing methods. Then, according to the research status at home and abroad, with the continuous wave ring cavity ringdown spectroscopy to focus on major issues closely related to the technology, in-depth research including the structure characteristics, ring beam and laser resonator with frequency matching, pattern matching, optical axis alignment, laser scanning and bandwidth characteristics the speed problem is established based on the spectral measurement of a complete system, and the application of a large number of experiments. On the basis of this, a series of factors that affect the accuracy of measurement are studied. The main contents of this paper and conclusions can be summarized as follows: (1) the high quality passive cavity is composed of two plane mirrors a spherical mirror cavity ringdown spectroscopy measurement technology based on some problems are studied, including: first, the beam characteristics of the triangular ring cavity is analyzed. The obtained beam the characteristics, frequency characteristics and optical cavity of circular polarization, a solid theoretical foundation for the application of ring resonators, and provides theoretical guidance for the design of the measurement system is good in the future; secondly, in order to reduce the Gauss beam and resonator coupling process, misalignment and mismatch effect on passive resonator measurement the technical precision based on the Gauss beam transformation rules, mode coupling theory and related beam propagation coordinate transformation theory, influence of misalignment and mismatch of mode coupling efficiency points Don't analyze and simulation, and gives a general expression reference volume two exist at the same time the fundamental mode coupling efficiency; thirdly, the beam propagation coordinate transformation angle, analyzes the existing condition of the conjugate axis resonant cavity is composed of a plurality of plane mirror, the odd mirror cavity only when the same the verticality with high precision plane mirror between the optical axis and is closed, even the plane mirror cavity there is always closed the optical axis of the conclusion, and gives the relationship between the change of cavity mirror with conjugate axis direction disorders and angle. The design parameters and basis of the resonant cavity are given. The paper analyzed the existing closed conjugate ring resonator optical axis triangle composed of two plane mirror and a spherical mirror. The results show that, when the angle deviation of different mirror, the cavity axis still exists conjugate closed, and gives the corresponding change of cavity axis and new resonance surface position and direction, thus because of adding spherical mirror reduces the existence of a plane mirror between the high precision parallel degree requirements resonator conjugate axis, to provide theoretical guidance for high precision alignment work spectral measurement technique based on high quality optical cavity; finally, this paper from the perspective of frequency, the frequency characteristic of incident light, because simple frequency matching can not be better for the frequency characteristics of the incident laser proposed restriction analysis better, in order to facilitate the subsequent selection of the laser parameters determined from the optical stack The principle of the addition is analyzed from two angles of time domain and frequency domain respectively, and the process of intracavity optical interference is given, which provides a theoretical basis for analyzing the characteristics of the optical field in the cavity, so as to facilitate the theoretical analysis of the problems that may be encountered. (2) on the basis of sufficient theoretical analysis, a continuous wave ring ring cavity ring down spectroscopy measurement scheme is set up. According to the theoretical analysis results of the ring cavity, the design of the whole measurement system, the control system design, the circuit design and the realization of hardware and software of the continuous wave cavity ring down spectroscopy system are introduced. This system has the following advantages and innovation, among them, using a distributed feedback (DFB) laser as light source, wavelength of the laser, the temperature tuning characteristics of tunable current so as to realize the "turn off", omitting related devices and optical switch; measuring system based on triangle ring cavity as resonant cavity is reduced direct return to the optical surface laser, eliminating the optical isolator; control system with high precision laser wavelength meter complete frequency adjustment and locking, under the premise of ensuring accuracy, locking phase modulation lock light resonance cavity with a series of laser resonator based on commonly used and omitted. Based on the established measurement system, the relevant design parameters are determined, and the performance of each component in the measurement system is tested. The main result is the laser turn off.
【学位授予单位】：中国科学院研究生院(长春光学精密机械与物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN248
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本文编号：1341009