强光光学元件零缺陷加工理论及关键工艺研究

Improving the load capacity of large laser driver system is ritical to Inertial Confinement Fusion (ICF). The accountability Bureau of USA independent investigation concluded: processing defect induced damage threshold decline is one of three major science and technology challenge to realize ICF. Large laser driver system using a large number of fused quartz material optical elements, its intrinsic threshold reached more than 150 joules per square centimeter, but after processing can achieve only about 2 Joule, processing defects are the main factor of decreasing the laser induced damage threshold (LIDT). Research shows, brittle and plastic removal cracks, scratches are fatal flaws. These defects, if not effectively removal and inhibition, will affect the LIDT threshold increase. The project put forward the material removal process in elastic region, due to not cause brittle and plastic changes, the processing will not bring fatal flaw, can achieve damage free processing. Mainly carried out elastic domain processing mechanism, implementation condition, processing method and in the entire process of optimization and other key technology research, is committed to improving the LIDT. Through the innovation process, to achieve more than 8 joules per square cm laser flux, meet the practical requirements of ICF system.

高通量条件下光学元件不发生激光损伤而稳定运行是激光核聚变系统点火成功的关键。熔石英光学元件大量应用在激光核聚变系统，材料本征激光损伤阈值约为150J/cm^2，但实际加工元件仅为2J/cm^2。美国政府调查表明，加工引入缺陷而导致阈值下降是国家点火装置面临的三大挑战之一。材料脆性和塑性去除产生的裂纹、划痕是致命缺陷，若不能有效抑制或去除将严重制约阈值的提高。项目针对熔石英材料创新提出弹性域去除加工方法：引入增强化学反应提高硅氧键能弱化效率，发明动压浮动抛光装置实现弹性域去除，革新抛光盘结构实现化学反应与弹性域去除一体化。由于去除过程不引起材料脆性和塑性变化，故有望实现零缺陷加工。主要探索弱化硅氧键能的化学机制、弹性域材料去除的基本条件以及原有缺陷的演变规律等科学问题。通过创新弹性域去除工艺理论与方法，实现零缺陷加工，优化现行工艺流程，满足激光核聚变系统8J/cm^2的激光损伤阈值设计要求。

高通量条件下光学元件不发生激光损伤而稳定运行是激光核聚变系统点火成功的关键。熔石英光学元件大量应用在激光核聚变系统，材料本征激光损伤阈值约为150J/cm^2，但实际加工元件仅为 2J/cm^2。美国政府调查表明，加工引入缺陷而导致阈值下降是国家点火装置面临的三大挑战之一。 材料脆性和塑性去除产生的裂纹、 划痕是致命缺陷，若不能有效抑制或去除将严重制约阈值的提高。项目深入探讨了界面化学吸附以及过程中光学元件表层原子键能弱化的规律，弹性域去除的临界条件；详细设计了流体动压超光滑加工装置实现光学材料弹性域去除；重点研究了加工过程中材料去除特性、 加工工艺优化以及材料的可加工性等关键问题。针对不同应用需求，开展加工实验。实验结果表明流体动压超光滑加工具有明显的表面质量提升能力：加工表面粗糙度 Rms 已经接近 0.1nm 的原子级超光滑水平；流体动压超光滑加工对低频面形精度具有优良的保持性能，对中高频表面粗糙度具有明显的抑制能力；加工表面粗糙度降低、 表面损伤减少，损伤阈值明显提高。