非线性晶体高功率紫外损伤机理与抗损伤技术探究

Damage of nonlinear crystal (LBO) under irradiation of high power UV laser is the bottleneck of UV laser industrialization. Traditional solution to improve the UV laser life is to change the incident spot or keep the output light travel at Brewster angle with uncoated crystal surface. However, the beam quality degrades as the UV laser output power drops, which is a fatal problem in high precision mirco-nano processing. Therefore, it is the central issue of high power UV laser to study the damage mechanism of nonlinear crystal under the incidence of high UV laser, and figure out new ways to avoid the damage and thus increase the life of single spot on the crystal surface. This project based on the Mie scattering theory analyzes the effects of electric field enhancement caused by surface residue, micro defect and the subsurface damage of nonlinear crystal, and then studies the damage mechanism of nonlinear crystal surface induced by the irradiation of high power UV laser. The project puts forward new ways to improve the damage resistance of nonlinear crystal surface such as the ultra-smooth surface machining and residue removal method, establishes the quantitative relationship between the surface characteristic parameters of nonlinear crystal and the UV laser life, provides the machining requirements of the nonlinear crystal respecting to a life standard under the given UV laser power, breaks through the technical bottleneck that limits the life of UV laser. It has very important theoretical research sense and practical application value to promote the industrialization of ultraviolet laser.

非线性晶体（LBO）高功率条件下紫外损伤问题是紫外激光器产业化的技术瓶颈，传统的办法是通过"换点"或者布儒斯特角输出不镀膜方式提高紫外激光器寿命，带来的问题是紫外激光功率在下降的过程中，光束质量也不断恶化，这对高精度微纳加工而言是致命的，因此研究非线性晶体高功率条件下紫外损伤机理，找到避免损伤的新方法，提高单点寿命是高功率紫外激光器的核心问题。本项目提出了通过Mie散射理论分析非线性晶体表面残留、微缺陷以及亚表面损伤等因素导致的电场增强效应，进而研究在高功率条件下引起非线性晶体表面损伤的机理，提出超平滑表面加工和残留去除等是提高非线性晶体表面抗损伤的重要手段，建立非线性晶体表面特征参数与紫外激光器寿命的定量关系，对于给定功率条件下的寿命指标给出非线性晶体表面加工要求，突破影响紫外激光器寿命的技术瓶颈。对于推进紫外激光器产业化具有重要的理论研究意义和实际应用价值。

高功率紫外固体激光器长时间工作稳定性问题是制约其发展和应用的重大瓶颈。本项目正是围绕解决这一核心问题而展开。首先，基于Mie散射理论模型，分析了抛光层残留颗粒对入射电场的增强效应，建立了分析吸收核心非稳态传热状况的微分方程，并对电场增强效应和引起的温度变化进行了仿真计算，得出了对于研究LBO晶体的表面损伤非常有意义的研究结果；其次，基于化学机械抛光技术，研究了LBO晶体超精密的抛光加工工艺，采用纳米SiO2抛光液和碳纳米金刚石抛光液在LBO晶体表面获得了超光滑表面RMS约0.5nm，显著减少了抛光层中残留的CeO2、SiO2等吸收核心。最后，搭建了LBO晶体损伤测试实验装置，研究了LBO晶体输出端面在高功率三倍频照射过程中的损伤问题，发现了Si元素的显著沉积，根据XPS实验探测到的结合能位于102.9 eV的Si (2p)峰，推断该元素以SiOxCy化合物形态存在，为解释LBO晶体在远低于损伤阈值的长时间紫外照射过程中的损伤问题提供了有力的依据。.本项目在执行过程中，在国内外重要光学期刊上已发表SCI收录论文10篇，获得授权发明专利2项，研究成果作为主要内容获得教育部自然科学奖二等奖1项，培养了3名博士研究生。