光学材料激光初始损伤的分子动力学模型研究

Along with the continuous progress of the Q-switching and model-locking technologies, the durations of ultra-short optical pulses has been successfully compressed from ns and ps to the order of fs. And supported by the amplifier technologies of the chirp pulses, the peak power of laser pulses has been successfully increased by several orders. As a result, the research on the interaction between laser and materials has been advanced to completely new stage. The damage of optical part has already become the bottleneck of high-energy, high-power lasers. Therefore, it is of significant and valuable about study the damage of optical parts resulted by lasers. The damage of optical material resulted by pulsed laser is a complex process, it is often accompanied the emergence of several coupling mechanisms..Generally, for ns and ps lasers, the major problem is how to keep the lasers working steadily for a long time. On other words, people have to deal with the problem of damages of various optical resulted by laser radiations. The optical components may include many kinds of reflectors, lens and windows, which are very useful in the laser systems. Of course, the components may also include various optoelectronics components. . .It has been proved by many experimental researches that the damage threshold of most optical components and materials obeys the famous 1/2τlaw when the laser pulse width (FWHM) τ is larger than 10ps, which means that the laser damage threshold of the materials, in unit of J/cm2, is approximately proportional to 1/2τ. It has been confirmed that this scaling law is the natural result of the classical Fourier thermal conduction theory. However, when the FWHM of the laser pulse becomes shorter than about 10ps, the laser damage threshold of the materials disobeys the 1/2τlaw. This suggests that fs laser damage of materials cannot be treated by the classical Fourier thermal conduction theory. .Presently, the design of laser instrument still lies in the empirical stage with little is known about the initialization of damage which constraint the further improving of stability. The high-speed-transient of laser radiation and the difficult of verifying makes there are no acceptable damage-initialization theory for optical materials..This application aims at uncover the mechanism of initialization of damage in optical material induced by laser radiation, investigate the key issue on molecular dynamics simulation include model building, potential energy, analyzing the microscopic response of electron, the effect of temperature rise and the damage character, put forward the criterion for initialization of laser-induced-damage.

激光器功率水平的提高对光学材料抗激光能力的要求越来越高，测定以及提高光学材料和光学元件的抗激光损伤能力具有重要意义。激光与材料之间的耦合机制非常复杂，激光辐照致光学材料损伤的实质是材料内部粒子或原子的离散动力学行为导致微观结构的破坏。激光辐照致光学材料损伤过程的高速瞬态性不宜表征和纳米尺度实验验证困难，材料的原子级迁移行为尚不明确，这些因素导致目前还未形成公认的光学晶体材料初始损伤理论。.本申请以研究揭示典型波长/脉宽激光辐照条件下光学材料初始损伤机理和规律为目标，围绕分子动力学几何物理建模及其解算、模拟结果实验验证及模型完善、初始损伤辨识等关键问题，分析构建能够精准表征光学材料结构损伤特征的分子动力学模型；研究短脉冲激光辐照下光学材料内的电子微观响应以及破坏过程、温升效应及损伤特性、材料内的强瞬态热效应,在此基础上提出典型光学材料激光初始损伤的科学判据，为工程应用提供理论指导。

激光技术的发展和激光器功率水平的提高对光学材料抗激光损伤能力的要求越来越高，测定以及提高光学材料和光学元件的抗激光损伤能力具有重要意义。激光导致光学器件的损伤已经成为发展更高功率激光器的关键限制因素，光学器件的抗激光损伤能力成为决定激光器性能的最重要因素之一，研究激光对光学材料的破坏机制及破坏阈值可为评估定向能激光束对目标的杀伤效果提供理论依据。.激光损伤研究的目的主要有两点：一是探讨损伤机理，对激光损伤与材料性质、结构、成分、制备工艺和加工方法等因素的关系进行系统研究，分析激光波长和脉宽等因素对损伤的影响，从而引导人们去发现更优的材料品种、制备工艺和加工方法；二是从实际应用出发，在实验室条件下模拟实际使用情况，测定损伤数据，研究特定情况下经典元件的损伤规律，为工程应用提供参考。激光辐照对光学材料的损伤是一个复杂的过程，主要由激光参数和材料性质两方面决定：不同的激光操作参数如波长、脉宽、偏振状态、光斑尺寸等对同一种物质会产生不同的损伤结果，同一激光操作参数作用下不同性质的材料会出现不同的损伤情况。.激光辐照损伤包括多方面的作用机理，如光热作用、光化学作用、光电作用和等离子体作用等，这些作用都在很短时间内产生，进一步增加了研究的难度。激光惯性约束核聚变实验装置中的石英材料作为非常重要的窗口材料，其抗激光损伤阈值和对激光束传输质量的影响是核聚变实验成败的关键要素。本项目以研究揭示典型波长/脉宽激光辐照条件下光学材料初始损伤机理和规律为目标，完成了分子动力学几何物理建模及其解算、模拟结果实验验证及模型完善、初始损伤辨识等关键问题，分析构建能够精准表征光学材料结构损伤特征的分子动力学模型；研究短脉冲激光辐照下光学材料内的电子微观响应以及破坏过程、温升效应及损伤特性、材料内的强瞬态热效应,在此基础上提出典型光学材料激光初始损伤的科学判据，为提高激光惯性约束核聚变装置中光学元件的负载能力提供理论支撑。