高反射率精密测量技术研究

发布时间：2018-08-28 14:06

【摘要】：光腔衰荡技术是一种基于高精细度光学谐振腔的高精度、高灵敏度光学检测技术。自上世纪70年代以来,经过多年发展,该技术已经在多个研究领域体现了重要作用,尤其是对于高反射率测量而言,是目前唯一能精密测量高反射率的方法。本论文着眼于光腔衰荡高反射率测量技术的工程化和仪器化,针对光腔衰荡时间常数提取和衰荡腔调节这两大问题,进行了相关研究。本文分析了理想高斯噪声条件下的光腔衰荡时间常数提取问题,对典型提取算法进行了理论分析和性能对比。着重关注了提取精度、提取准确度和运算量这三方面的性能。理论分析和对比表明,非线性最小二乘方法具有最好的提取精度和准确度,但是运算量开销较大,提取光腔衰荡时间常数的耗时较长。为了进一步提升衰荡时间常数的提取效率,对加权线性最小二乘算法进行了改进,提出一种数据点筛选方法,实现了高精度、快速同时误差较小的衰荡时间提取。同时,探究了一种基于空间滤波平滑技术的信号预处理方法,改善了低信噪比信号的提取效果。本文进一步考虑了光腔衰荡系统对衰荡信号的调制作用,分析了几种典型调制因素对衰荡时间提取的影响,比如系统上升时间、系统背景噪声以及数据采集卡的采样分辨率。系统上升时间将造成额外的衰荡时间提取误差,因此其调制影响最为明显。理论推导发现,加权线性最小二乘拟合算法的拟合偏差与系统上升时间偏移项造成的偏差在一定条件下能够相互抵消,由此可以实现了高精度和高准确度的衰荡时间提取。另外,实际系统背景噪声的分布形式十分复杂,其中包含高斯噪声,也包含一定比重的泊松噪声。针对不同分布形式的背景噪声进行了仿真分析,发现系统背景噪声分布形式对衰荡时间提取影响不大,只要保证信噪比,那么衰荡时间的提取结果在不同噪声背景下都基本一致。数据采集卡的采样分辨率对信号分析有一定的影响,不过当数据采集卡采样深度在10bit以上时,影响在可承受范围内。在衰荡腔调节方面,本文分析了腔参数失调导致的模式耦合,并利用角谱传播理论分析了模式耦合导致的多横模运行对测量的影响。结果发现多横模状态和基横模状态的损耗在同一量级且差异较小,因此我们得出结论:多横模运行对腔损耗的测量影响有限。不过,腔参数失调仍会改变腔损耗大小,所以精密调腔十分必要。于是对现有调腔评价方法进行了介绍和简要讨论,主要介绍了腔透射信号峰值、腔透射脉冲波形包络和透射光相位延迟这3种调腔评价方法,尤其考虑了这些调腔方法的工程化适用性。对适于仪器化和自动化的调腔评价标准进行了探究,对腔结构优化进行了简单考虑,提出一种基于平凹稳定腔的腔结构方案。本文着重分析了光腔衰荡时间常数的提取,并初步探究了衰荡腔调节问题,对于光腔衰荡高反射率测量技术的工程化和仪器化具有指导意义,对于光腔衰荡技术在其它领域的应用也具备一定的参考作用。
[Abstract]:Cavity ring-down technology is a high-precision, high-sensitivity optical detection technology based on high-precision optical resonator. Since the 1970s, after years of development, this technology has played an important role in a number of research areas, especially for high-reflectivity measurement, is the only accurate method to measure high-reflectivity. This paper focuses on the engineering and instrumentalization of cavity ring-down high reflectivity measurement technology, and studies the extraction of cavity ring-down time constant and the adjustment of cavity ring-down time constant. The theoretical analysis and comparison show that the nonlinear least squares method has the best extraction accuracy and accuracy, but the computational cost is large, and the time-consuming of extracting the cavity ring-down time constant is longer. The extraction efficiency is improved by the weighted linear least squares algorithm, and a data point selection method is proposed to achieve high precision, fast and small error of the extraction of the decay time. At the same time, a signal pre-processing method based on spatial filtering and smoothing technology is explored to improve the low signal-to-noise ratio signal extraction effect. Considering the modulation effect of the cavity ring-down system on the ring-down signal, the influence of several typical modulation factors on the extraction of the ring-down time is analyzed, such as the rise time of the system, the background noise of the system and the sampling resolution of the data acquisition card. Theoretical deduction shows that the deviation caused by the fitting deviation of the weighted linear least squares fitting algorithm and the system rise time offset term can cancel each other under certain conditions, thus realizing the extraction of high precision and high accuracy of the ring down time. Noise also contains a certain proportion of Poisson noise. The simulation analysis of different distribution of background noise shows that the distribution of system background noise has little effect on the extraction of ring-down time. As long as the signal-to-noise ratio is guaranteed, the extraction results of ring-down time are basically the same in different noise background. Resolution has a certain influence on signal analysis, but when the sampling depth of the data acquisition card is above 10 bit, the influence is within the acceptable range. In the regulation of ring-down cavity, the mode coupling caused by cavity parameter misalignment is analyzed, and the influence of mode coupling caused by multi-transverse mode operation on measurement is analyzed by using angular spectrum propagation theory. Now the loss of multi-transverse mode and base transverse mode is the same order of magnitude and the difference is small, so we come to the conclusion that the influence of multi-transverse mode operation on cavity loss measurement is limited. However, the cavity parameter misalignment will still change the cavity loss, so it is necessary to adjust the cavity precisely. Three evaluation methods of cavity tuning are introduced, including peak value of cavity transmission signal, envelope of cavity transmission pulse and phase delay of transmitted light. Especially, the engineering applicability of these methods is considered. In this paper, the extraction of cavity ring-down time constant is emphatically analyzed, and the adjustment of cavity ring-down is preliminarily explored. It is of guiding significance for the engineering and instrumentalization of cavity ring-down high reflectivity measurement technology, and also has certain reference value for the application of cavity ring-down technology in other fields.
【学位授予单位】：中国科学院研究生院(光电技术研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TP274

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