熔石英体内杂质对激光光场调制的研究

发布时间：2018-05-30 19:31

本文选题：熔石英光学材料 + Mie理论　；参考：《西南科技大学》2015年硕士论文

【摘要】：激光应用于惯性约束核聚变的设想被提出及理论和技术上得到证实后,大型激光驱动系统的研制受到许多国家的重视。光学元件的抗损伤能力一直是制约高功率激光系统发展的一个瓶颈,其表面及体内含有的各种缺陷是诱导光学元件损伤的主要原因之一。熔石英光学材料是激光系统中常用的光学元件原材料之一,在材料熔炼及元件加工过程中难以避免地会引入杂质颗粒。杂质颗粒对入射激光的吸收和调制会导致光学元件损伤阈值下降。目前对杂质热效应已有深入研究和共识,而关于杂质对入射光场调制作用的研究不多而且没有给出一个定量的关系。本文针对熔石英内球形杂质颗粒对入射光场的调制作用,进行了理论建模和计算分析。论文的主要研究内容和结果如下:基于Mie散射理论,建立了熔石英体内球形杂质颗粒对入射光场调制的三维模型,针对杂质参数(尺寸、折射率)和激光参数(波长、平面波、高斯波束)对调制光场的影响进行了计算仿真和分析。研究结果表明,对于波长为355 nm的平面波入射,如果杂质颗粒的半径小于?/10,杂质对光场的调制影响不大,可以忽略。当颗粒半径大于?/10时,对非耗散杂质,光强增强因子(light intensity enhancement factor,LIEF)随杂质折射率与熔石英折射率差值的增大而增大,局部可以达到102量级。当折射率小于熔石英的折射率时,后向散射强于前向散射;对于耗散杂质,其折射率虚部越大,LIEF受折射率实部的影响越小,前向散射强度随杂质颗粒半径的增大先上升后下降,当半径大于?/2时,后向散射随杂质颗粒半径增大而增大,且后向散射强于前向散射。光强最强处的位置距杂质颗粒表面的最近距离L受杂质的折射率和半径的影响。对于高斯波束入射,杂质周围光强分布规律与平面波类似,但是束腰半径对LIEF的影响较大,当高斯波束的束腰半径大于10倍波长时,可以将高斯波束入射退化为平面波入射的情况。总之,杂质就像埋藏在熔石英内部的微透镜,它对入射光场调制引起局部光场增强对光学元件的损伤有很大的影响。本文结果对于实际应用中熔石英的处理有一定的指导意义,在光学元件制备过程中降低杂质颗粒含量,特别是大尺寸颗粒,可以有效的提高光学元件的抗激光损伤能力从而延长其使用寿命。
[Abstract]:After the idea of laser application in inertial confinement fusion has been put forward and proved theoretically and technically, the development of large laser drive system has received much attention in many countries. The anti-damage ability of optical elements has been a bottleneck restricting the development of high-power laser systems. The defects in the surface and body are one of the main reasons to induce the damage of optical elements. Fused quartz optical material is one of the commonly used raw materials of optical elements in laser system. Impurity particles are inevitably introduced in the process of material melting and element processing. The absorption and modulation of impurity particles to the incident laser will decrease the damage threshold of optical elements. At present, the thermal effect of impurity has been deeply studied and agreed, but there is not much research on the effect of impurity on the modulation of incident light field, and there is not a quantitative relation. In this paper, the modulating effect of spherical impurity particles on incident light field in fused quartz is studied. The main contents and results of this paper are as follows: based on Mie scattering theory, a three-dimensional model for the modulation of incident light by spherical impurity particles in fused quartz is established. The impurity parameters (size, refractive index) and laser parameters (wavelength, plane wave) are studied. The effect of Gao Si beam on the modulated light field is simulated and analyzed. The results show that if the radius of impurity particles is less than 10, the impurity has little effect on the modulation of light field, which can be neglected. For non-dissipative impurities, the light intensity enhancement factor (light intensity enhancement factor) increases with the increase of the difference between the refractive index of impurity and the refractive index of fused quartz when the particle radius is larger than / 10:00, and the local value can reach 102 orders of magnitude. When the refractive index is smaller than the refractive index of fused quartz, the backward scattering is stronger than the forward scattering, and for the dissipative impurity, the larger the refractive index imaginary part is, the smaller the effect of the refractive index real part is, and the forward scattering intensity increases first and then decreases with the increase of impurity particle radius. When the radius is larger than 2, the backscattering increases with the increase of the radius of impurity particles, and the backscattering is stronger than the forward scattering. The nearest distance from the strongest position to the surface of impurity particle L is affected by the refractive index and radius of impurity. For the incidence of Gao Si beam, the distribution of light intensity around the impurity is similar to that of plane wave, but the beam waist radius has a great effect on LIEF. When the beam waist radius of Gao Si beam is more than 10 times wavelength, The incidence of Gao Si beam can be reduced to plane wave incidence. In a word the impurity is like a microlens embedded in the fused quartz which has a great influence on the damage of the optical element caused by the local light field enhancement caused by the modulation of the incident light field. The results of this paper have certain guiding significance for the treatment of fused quartz in practical application, and reduce the content of impurity particles, especially the large size particles, in the process of fabrication of optical elements. It can effectively improve the ability of optical elements to resist laser damage and prolong their service life.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN249

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