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题名:
激光量热和光热联合技术测量光学样品吸收和热变形方法研究
作者: 刘明强
学位类别: 硕士
答辩日期: 2008-06-06
授予单位: 中国科学院光电技术研究所
授予地点: 光电技术研究所
导师: 李斌成
关键词: 吸收测量 ; 表面热变形 ; 激光量热法 ; 表面热透镜 ; 薄膜
其他题名: Combined laser calorimetry and photothermal technique for absorptance and thermal deformation measurements of an optical coating
学位专业: 光学工程
中文摘要: 随着高功率激光器及激光系统的不断发展,作用到光学元件表面越来越高的功率密度(MW/cm2)或者能量密度(10J/cm2及以上)已对薄膜元件的性能提出了很苛刻的要求。薄膜元件的吸收损耗和表面热变形对入射激光的能量和光束质量的影响,已成为高功率激光发展的瓶颈。只有优化镀膜工艺和提高光学元件质量,尽量降低元件对入射激光的吸收,才能满足高功率激光发展的要求。因此,首先要研究一种能同时检测光学薄膜样品的吸收率和热致表面变形的测量方法。本文中提出了激光量热(Laser Calorimetry, LC)和光热(表面热透镜技术(Surface Thermal Lens, STL))联合技术用于同时测量光学薄膜样品的弱吸收和纳米级及以下热变形的方法,这将使薄膜样品的吸收和热变形两个重要参数得到有效衡量,并可用于研究样品的热学以及热物理性质。 本文首先(第一章)简述了薄膜吸收和热变形的来源和机理;紧接着对测量吸收的常用方法(如分光光度计法,光热法和量热法等)做了介绍,并阐述了激光量热法的发展和原理,为后文用其进行吸收测量做好铺垫;对测量热变形的常用方法(激光干涉法,哈特曼波前传感法以及光热法等)也做了简要描述,给出了表面热透镜技术用于热变形测量的原理。 本文第二部分(第二、三章)描述了表面热透镜信号和激光量热信号的理论模型。根据热传导和热弹性方程,推导了光学薄膜样品在方波调制的高斯和平顶激励光作用下的温度场,表面热变形场和表面热透镜信号模型。然后,利用Fortran程序对温度、热变形和STL信号随样品和激励光参数在时域、频域和空域中的变化情况进行了数值模拟,分析了其变化规律。同时,将温度和热变形的有限元Ansys模拟结果与前述数值模拟结果进行了比较,获得了较好的一致。 第三部分(第四章)为LC和STL联合技术的实验部分。首先搭建了联合实验平台,介绍了联合系统的结构,并总结了在系统搭建过程中需要注意的一些问题。根据理论模拟结果对系统进行了优化,然后对一组1064&632.8nm @ 0oHR、基底为BK7的样品进行了测试,分析了样品的温升和吸收情况。在作用到样品上功率为2.6W的情况下,获得了LC和STL的探测灵敏度分别为1.2×10-6和0.5×10-6。并从STL信号的幅度和相位对光学样品的热稳定性进行了研究。同时对STL信号和表面热变形进行了讨论和计算。对一吸收为1320ppm的样品,获得了其表面交流形变为1.16 nm,直流形变为11.8nm。并将前面的形变和理论计算的结果进行了比较,分析了实验结果的合理性。通过进一步的研究和改进,该联合系统将可用于吸收和表面热变形的准确测量,而且在元件的光学和热物理稳定性研究方面也具有潜在的应用价值。 最后对论文工作进行了总结,对下一步工作提出了建议。
英文摘要: With rapid development of the high-power lasers, larger power densities (more than MW/cm2) or energy densities (over 10J/cm2) on the surfaces of optical components have imposed stringent requirement on the power-handling capability of these coatings. Laser-induced absorptance and thermal deformation are the two main factors which deteriorate the energy and beam-quality of the incident laser, and subsequently limit the further development of the high-power laser. In order to rule out the limitation, coating-deposition technique must be optimized so as to improve the performance of the optical components. First of all, a promising technique, which will be able to measure the low-absorptance and sub-nanometer thermal deformation of a coating simultaneously, should be developed. In this dissertation, a combined laser calorimetry (LC) and surface thermal lens technique (STL) is put forward. This will contribute to effectively evaluate two important parameters of the sample—the absorptance and thermal deformation, and also can be used to measure thermo-physical properties of the optical coating. In the first chapter, we formulated the mechanisms of the absorption and thermal deformation and a brief introduction to the absorption-measurement methods (such as the spectrophotometry, photothermal methods and laser calorimetry) was followed. Especially, the development and principle of the laser calorimetry was introduced in detail to lay a basis for later use in absorption measurement. Then, we also described the common methods employed to carry out the deformation measurement (i.e., laser interferometry, Hartmann wave-front sensing method and photothermal methods) and discussed the principle of STL technique on the deformation measurement. In the second part (including chapter 2 and 3), theoretical models of the STL signal and the LC signal are described separately. According to the thermal conduction and thermal-elastic equations, the temperature and thermal deformation fields of an optical coating, irradiated by a square-wave modulated top-hat or Gaussian beam excitations, are deduced. The STL signal model was also defined subsequently. Then, the temperature, thermal deformation and STL signal in time-, frequency- and space-domains are numerically simulated via programs written in Fortran language, and their variations with different parameters are analyzed. In the meantime, simulation results of the analytical temperature and deformation distributions are also compared with that calculated by finite-element analysis software—Ansys, and good agreements are obtained. Part 3 of this dissertation is an elaboration of the combined technique and its application in the experiment. The combined experimental setup was found firstly and an introduction to its structure was followed. Then, we summarized some aspects to which should be paid attention in the course of system construction. The combined system was optimized according to the guide of the theoretical simulation results, and then a set of samples (1064&632.8nm@0oHR, substrate BK7) were measured. At first, the temperature rise (absorptance) and STL amplitude of one sample were analyzed for different laser parameters (including the laser power, irradiation time, modulation frequency). With a modulated irradiation power of 2.6W, the limits of detection for the LC and STL techniques are approximately 1.2×10-6 and 0.5×10-6, respectively. In the second, from the STL amplitude and phase, we studied stabilization of the thermal and thermo-physical properties of a sample irradiated with a relatively higher power in a period of long time. In addition, we calculated the thermal deformation of one sample according to the relation of the STL amplitude and thermal deformation defined in chapter 2, and for a sample with absorptance 1320ppm, the AC and DC deformations are determined to be 1.16nm and 11.8nm, respectively. The experimental result was compared with the theoretical case in which the deformation is worked out according to the deformation formula, and the rationality of the result was also analyzed. Through further study, this combined system will possess a potential application value in the measurement of the absorptance, thermal deformation and other sample properties, and in the research of optical and thermo-physical stabilization of an optical component. Finally, we summarized the contents of this dissertation and give some advices for further research.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ioe.ac.cn/handle/181551/301
Appears in Collections:光电技术研究所博硕士论文_学位论文

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Recommended Citation:
刘明强. 激光量热和光热联合技术测量光学样品吸收和热变形方法研究[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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