IOE OpenIR  > 光电技术研究所博硕士论文
Alternative TitleStudy on Photothermal Testing Method forWeak Absorption of Optical Coatings
Thesis Advisor李斌成
Degree Grantor中国科学院光电技术研究所
Place of Conferral光电技术研究所
Degree Discipline光学工程
Keyword微弱吸收 表面热透镜 光热形变 反射式和透射式 反射率温度系数 光热失调 灵敏度
Abstract光学薄膜是几乎所有光学系统中不可或缺的基本元件,薄膜元件光学性能的改善是提高光路系统整体性能的关键。吸收损耗是衡量光学薄膜性能的重要参数,它的存在,已成为限制高功率激光技术发展的一个重要因素。光学薄膜吸收损耗的准确测量,对膜层的优化设计、薄膜损伤机理的研究和镀膜工艺的提高具有重要意义。目前,激光量热技术和光热偏转技术、表面热透镜技术等光热技术已成功应用于光学薄膜微弱吸收测量领域。 本文进一步研究了热透镜技术中的几个问题,提出了一种测量光学薄膜吸收损耗的新方法,主要开展了如下工作: 介绍了表面热透镜技术中光热形变的近似和精确解表达式,并分析了两者以及相应的表面热透镜信号的差异,分析表明,近似解过高的估计了形变和相应的表面热透镜信号,只有在热扩散长度较小时误差较低,为近似解的实际应用及其合理性提供了理论依据。 介绍了热透镜技术中用于薄膜性能研究的反射式和透射式两种探测构型,并以BK7玻璃和石英为基底的样品进行了理论和实验分析,结果表明对BK7玻璃基底样品采用反射式探测构型较为灵敏,而对石英基底样品采用透射式探测构型较为灵敏,为两种测量方式的合理应用提供了依据。 在详细分析光学薄膜反射或透射光谱带因温度影响发生漂移现象的基础上,结合光热技术的基本理论,提出了一种测量光学薄膜吸收损耗的新方法-光热失调技术。根据理论模型,搭建实验平台,分别采用强度周期性调制的连续激光和脉冲激光作为激励光源,以高反射膜为样品进行了实验研究,成功获得了光热信号,实验结果与理论预计基本一致。与表面热透镜技术相比,光热失调技术降低了实验操作的难度,易实现信号的优化,稳定性和抗干扰能力有所提高;理论和实验结果表明在一定条件下光热失调技术可以获得比表面热透镜技术更高的测量灵敏度。光热失调技术的提出丰富了光热技术的理论和方法,可望在高功率激光系统中的光学薄膜性质研究领域得到广泛应用。
Other AbstractThe optical thin film coatings are the most basic components of optical systems. The improvement of the coating performance plays an important role in the improvement of the whole optical systems performance. Absorption is one of the important characters of coatings, which is a limiting factor in high-power laser applications. The sensitive absorption measurement is essential to the optimization of the film design, to the study of the laser-induced damage, and to the improvement of the deposition techniques. At present, laser calorimetry, photothermal deflection and surface thermal lens are widely used in absorption measurement of optical coatings. In this paper, some problems are discussed in thermal lens technique and a novel method is developed to measure the absorption of coated optical components. An explicit thermoelastic model and an approximate model to describe the photothermal deformation of a coated sample are presented. Numerical calculations are performed to investigate the differences between the explicit and approximate models in both surface displacement and STL signal. The simulation results show that the approximate model over-estimates the surface deformation and the corresponding STL signal amplitude. A decrease in thermal diffusion length reduces the differences between the results obtained with the two models. Those results provide a theoretical basis for the applications of the approximate model. The reflected TL and transmitted TL configurations are presented. The photothermal signal are theoretically and experimentally investigated in details with the optical dielectric coatings samples deposited on BK7 and fused silica substrates. Numerical and experimental results show that, for BK7 substrate coating, the reflected TL configuration has a higher sensitivity; but for fused silica substrate coating, the transmitted TL configuration has a higher sensitivity. Those results provide theoretical and experimental basis for the suitable application of the two detection configurations. Based on the analysis of the temperature-induced shift of reflectance or transmission spectrum of an optical coating, utilizing the theory of the photothermal technique, a novel photothermal technique-photothermal detuning is developed to measure the absorption of coated optical components. The theoretical description of the photothermal detuning signal with a continuous-wave modulated laser beam excitation and a pulsed laser beam excitation are presented. Experiments are conducted with a highly reflective coating to measure the photothermal detuning signal. Good agreements between the theoretical predictions and experimental results are obtained. Compared with surface thermal lens, this novel method reduces the experimental complexity, but the sensitivity is easy to be optimized. The stability and the anti-jamming are improved. The experimental and theoretical results show that the photothermal detuning technique can be used to obtain a higher measuremental sensitivity. The novel method is expected to find applications in optical coatings used in high-power laser applications.
Document Type学位论文
Recommended Citation
GB/T 7714
郝宏刚. 光学薄膜吸收的光热测量方法研究[D]. 光电技术研究所. 中国科学院光电技术研究所,2008.
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