高分辨中子衍射研究氘化KDP晶体微结构畸变规律及其诱导激光损伤的物理机制

Due to the significantly reduced stimulated Raman scattering effect by deuterium isotope substitution effect, deuterated KDP crystals is the best choice for third harmonic generation crystal materials of Megajoule level high-power laser facility. However, compared to KDP, the laser-induced damage threshold of DKDP crystal is severely degraded, which has become the bottle-neck problem to be solved. The basic physical problem is that deuteration induces the micro-structure distortion in DKDP crystal, and then causes the structure breakdown and macroscopic damage of materials under laser irradiation. There are two difficulties in studying the laser damage of deuterated KDP, first is how to precisely study the deuteration-induced micro-structure distortion, and second is how to correlate the micro-structure distortion with its macroscopic damage characteristics. In this project, the laws of micro-structure distortion such as the precise occupying position of deuterium atoms, the lattice constant, hydrogen (deuterium) bond and vacancy will be studied based on nuclear analysis techniques like high-resolution neutron diffraction. By studying the variation laws of micro-structure distortion under different laser irradiations, the breakdown mechanisms of deuterated KDP will be analyzed. Combining with the laser damage laws, we will build the physical correlation of deuteration, micro-structure distortion, materials breakdown mechanism with the macroscopic damage characteristics, and finally disclose the micro-structure distortion-induced laser damage mechanisms in deuterated KDP. Results will provide scientific basis both for crystal quality control and improvements of damage resistance. It also has practical significance for solving the bottle-neck problem of damage in deuterated KDP crystal of the laser facility.

氘化KDP晶体因氘化同位素替代效应，能够显著抑制KDP的受激拉曼散射，成为兆焦耳级高功率激光装置三倍频晶体材料的最佳选择。然而，相对于KDP，氘化KDP的激光损伤阈值严重降低，成为亟待解决的瓶颈问题。基本物理问题是：氘化诱导KDP产生微观结构畸变，进而诱导材料在激光辐照下的结构破坏和宏观损伤。目前的研究难点一是如何精确研究氘化诱导微观畸变，二是如何关联微观结构畸变和宏观损伤特性。本项目基于高分辨中子衍射等技术，研究氘原子的精确占位、晶格常数、氢（氘）键等化学键和空位缺陷等微结构畸变规律。通过研究微畸变在激光辐照下的演化规律，分析氘化晶体的破坏机制。结合激光损伤规律，建构氘化、微结构畸变、材料破坏机制、宏观损伤特性之间的物理关联，揭示氘化KDP微畸变诱导激光损伤的机制。研究成果将为氘化晶体质量控制及提升抗激光损伤能力提供科学基础，对解决高功率激光装置中DKDP损伤阈值低的瓶颈问题有现实意义。

氘化KDP晶体因氘化同位素替代效应，能够显著抑制KDP的受激拉曼散射，成为兆焦耳激光装置三倍频晶体材料的最佳选择。但是，氘化导致KDP晶体损伤阈值急剧降低的问题成为阻碍其获得实际应用的瓶颈。本项目利用高分辨衍射和核磁共振技术研究了氘化诱导KDP晶体的微观应变、化学键变化等微观结构畸变；利用同步辐射高分辨X射线、微束拉曼光谱、电子显微图像等技术研究了氘化KDP晶体在激光辐照下的晶相结构、化学键、缺陷、形貌变化，分析了氘含量的影响，初步获得了氘化引起KDP晶体微结构畸变的规律和氘化引起KDP晶体激光损伤的机制。结果表明：氘含量增加使晶体中o-H键和P-H键键长增加，（101）和（200）晶面的微观应变增加，导致PO4四面体发生畸变；晶相转变、材料表面分解是引起氘化KDP晶体激光损伤的两种重要机制；氘化晶体中的金属铜杂质缺陷是诱导激光损伤的关键缺陷。研究结果可为氘化KDP晶体的生长和加工过程质量控制以及抗激光损伤能力的提升提供科学基础和参考。