熔石英元件光学缺陷激光修复的动力学过程研究

发布时间：2018-08-28 14:13

【摘要】：对CO_2激光修复熔石英元件损伤的理论上的计算模拟,首先要建立修复元件损伤的物理过程的模型及对不同损伤形貌的几何模型。研究在同一激光参数下不同损伤尺寸的热力学和动力学过程;研究在同一损伤尺寸不同激光参数下的热力学和动力学过程。作为高通量段固体激光装置的首选材料熔石英,由激光导致的损伤依然是限制CO_2激光通量的主要因素。抑制元件表面损伤增加,是提高激光装置负载能力的一个重要方法。在众多修复损伤的方法中,普遍认同CO_2激光的修复效果,针对这种修复方案的物理过程展开了理论分析及数值计算,本文研究的主要内容及结论如下:1.总结了熔石英表面损伤的特点、类型。结果表明:可以从损伤形貌上将其划分为划痕型、麻点型、坑洞型等几种。从形成属性上可分为脆性、塑性以及两种属性相混的损伤形貌。损伤点的形貌与CO_2激光光束形状、大小和空间分布有直接关系。对常见的元件表面损伤形貌进行建模,运用传热和流动的耦合来确立激光辐照熔石英元件的熔融模型,定量的描述了熔石英元件修复过程中的表面特征。2.只改变一种CO_2激光的参数,保持其它参数不变情况下,探讨了多种激光参数对修复不同损伤形貌的结果。结果显示修复后的形貌,基本外形呈现高斯坑形,对修复结果的影响比较显著的激光参数有:激光辐照时间、光束形状和功率。脉冲频率对修复尺寸的影响则不大,但增加频率可显著的缓解熔石英材料的蒸发,而对熔石英材料的熔融区域影响不大,可使元件修复后的表面更加光滑。和现有的实验结论相符合。3.计算了高斯形光束辐照熔石英元件的温度的演化过程和温度分布。刚修复后,最高温度位于光斑中心,并由中心向外梯度下降,温度在材料表面的下降速度较快,而温度在材料内的的下降速度则较慢,材料表面的等温线呈环形,而元件内的等温线的深度相对较小、宽度相对较大。在修复过程中和和修复后的冷却降温过程中温度变化均是先快速降低,然后减缓。4.在模拟修复后冷却过程中采用蠕变理论来分析,用该理论分析熔石英材料的退火过程中的应力。通过模拟可知该理论可有效的分析退火过程中的应力。此外,通过对比可以发现在退火过程中可以用大光束的激光,这有利于提高熔石英元件修复后的表面光滑程度。5.计算了激光辐照元件的热应力的分布与演化,及激光参数如何影响应力分布。CO_2激光辐照过程中光斑所在区会产生压应力,而在光斑之外产生拉应力,修复后的降温过程恰恰相反。材料表层的主应力关于光斑中心呈圆形分散开,光束中心元件表面的最大拉应力处于光束外围。而材料表面的最大剪切应力有四个,它们关于光束的圆心对称,并且位于辐照边缘,形状相似。此外残余剪切应力的最大半径只与激光光束的半径有关,和现有的实验结论相符合。6.模拟计算了光束半径、激光功率、辐照时间三个激光参数如何影响修复过程中材料在熔融时的流动,结果显示,随辐照时间的延长,熔融材料的流速迅速上升,同时,凸起环高度和高斯坑深度也快速增加。此外,在元件相同的最高温度情况下,改变光束半径和激光功率对的流速影响均较小。随着激光单位面积功率增大,凸起环高度、高斯坑深度、宽度均有不同程度增大,然而,激光功率对坑深和环高影响更显著,而光束半径对坑深和环高影响较弱,但对坑宽的影响却较显著。
[Abstract]:In the theoretical calculation and Simulation of CO_2 laser repairing fused silica damage, the physical process model and the geometric model of different damage morphology should be established firstly. Dynamics and dynamics. Laser-induced damage to fused silica, the preferred material for high-throughput solid-state laser devices, remains a major limiting factor for CO_2 laser fluxes. The main contents and conclusions of this paper are as follows: 1. The characteristics and types of surface damage of fused silica are summarized. The results show that the surface damage can be divided into scratch type, pit type, pit type and so on. For brittleness, plasticity and mixing of two properties, the morphology of the damage point is directly related to the shape, size and spatial distribution of CO_2 laser beam. The surface characteristics of the repaired parts were studied by changing the parameters of one CO_2 laser and keeping the other parameters unchanged. The results show that the repaired parts have Gaussian pit shape, and the laser parameters have significant influence on the repaired results. Time, beam shape and power. Pulse frequency has little effect on the repairing size, but the evaporation of fused silica can be significantly alleviated by increasing pulse frequency, and the melting area of fused silica can be neglected. The surface of repaired fused silica can be smoother. It is consistent with the existing experimental results. 3. Calculated the irradiation of fused silica with Gaussian beam. Temperature evolution and temperature distribution of the element. After repair, the highest temperature is located in the center of the facula and decreases from the center to the outside gradient. The temperature decreases faster on the surface of the material, but the temperature decreases slower in the material. The isotherms on the surface of the material are annular, while the depth and width of the isotherms in the element are relatively small. In the process of repairing and cooling process after repairing, the temperature changes decrease rapidly first, and then slows down. 4. In the process of cooling after repairing, creep theory is used to analyze the stress in the annealing process of fused silica materials. The stress in the process of annealing can be improved by using a large beam of laser. 5. The thermal stress distribution and evolution of the laser irradiated element and how the laser parameters affect the stress distribution are calculated. The principal stress on the surface of the material is circularly dispersed with respect to the center of the spot, and the maximum tensile stress on the surface of the element at the center of the beam is at the periphery of the beam. In addition, the maximum radius of residual shear stress is only related to the radius of the laser beam, which is consistent with the existing experimental results. 6. The effects of three laser parameters, beam radius, laser power and irradiation time, on the flow of the material in the melting process are simulated and calculated. With the increase of the laser power per unit area, the height of the convex ring, the depth of the Gaussian pit and the depth of the convex ring increase rapidly. However, the influence of laser power on pit depth and ring height is more significant, while the influence of beam radius on pit depth and ring height is weaker, but on pit width is more significant.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN249

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