Wenyun Du 1,2Meiping Zhu 1,2,3,4,*Jun Shi 1,2,3Tianbao Liu 1,2[ ... ]Jianda Shao 1,2,3,4
Author Affiliations
Abstract
1 Laboratory of Thin Film Optics, Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, China
2 Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing, China
3 Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China
4 CAS Center for Excellence in Ultra-intense Laser Science, Shanghai, China
The laser-induced damage threshold (LIDT) of plate laser beam splitter (PLBS) coatings is closely related to the subsurface absorption defects of the substrate. Herein, a two-step deposition temperature method is proposed to understand the effect of substrate subsurface impurity defects on the LIDT of PLBS coatings. Firstly, BK7 substrates are heat-treated at three different temperatures. The surface morphology and subsurface impurity defect distribution of the substrate before and after the heat treatment are compared. Then, a PLBS coating consisting of alternating HfO2–Al2O3 mixture and SiO2 layers is designed to achieve a beam-splitting ratio (transmittance to reflectance, s-polarized light) of approximately 50:50 at 1053 nm and an angle of incidence of 45°, and it is prepared under four different deposition processes. The experimental and simulation results show that the subsurface impurity defects of the substrate migrate to the surface and accumulate on the surface during the heat treatment, and become absorption defect sources or nodule defect seeds in the coating, reducing the LIDT of the coating. The higher the heat treatment temperature, the more evident the migration and accumulation of impurity defects. A lower deposition temperature (at which the coating can be fully oxidized) helps to improve the LIDT of the PLBS coating. When the deposition temperature is 140°C, the LIDT (s-polarized light, wavelength: 1064 nm, pulse width: 9 ns, incident angle: 45°) of the PLBS coating is 26.2 J/cm2, which is approximately 6.7 times that of the PLBS coating deposited at 200°C. We believe that the investigation into the laser damage mechanism of PLBS coatings will help to improve the LIDT of coatings with partial or high transmittance at laser wavelengths.
laser-induced damage threshold nodule defect plate laser beam splitter subsurface impurity defect High Power Laser Science and Engineering
2023, 11(5): 05000e61
1 电磁空间安全全国重点实验室，天冿 300308
2 电子科技大学 物理学院，成都 610054
3 中国工程物理研究院 激光聚变研究中心，四川 绵阳 621900
改进了描述光学材料强激光损伤的吸收波前模型，在原有模型的基础上引入了杂质缺陷吸收项，并将一维形式推广到了三维。利用改进后的吸收波前模型，数值模拟了红外单晶硅光学材料在波长1064 nm皮秒激光辐照时杂质源（以金属铁为例）附近材料的温度、损伤半径及损伤阈值等变化情况，并分析了光学材料初始温度对损伤阈值的影响规律。数值结果显示：（1）与传统的热传递模型不同，在损伤阈值附近，激光场能量密度从低于损伤到达到（或超出）损伤的微小变化导致温度场的巨大变化；（2）达到损伤能量密度后，杂质附近的最高温度及利用吸收波前表征的材料损伤半径随着辐照能量密度的增加近似线性增长；（3）激光损伤阈值随着材料初始温度的增加而降低。研究结果表明改进后的吸收波前模型可以较好地描述光学材料的杂质缺陷诱导强激光损伤：相比于传统的热超导模型，吸收波前模型可以更合理的表示损伤阈值附近温度场的突变，并可定量分析杂质诱导光学材料的强激光损伤尺寸。另外对单晶硅吸收波前模型的研究还显示提升材料的初始温度可以有效降低材料的强激光损伤阈值，这为提升光电对抗中光电探测器的激光损伤效率提供了一种思路。
杂质缺陷 光学材料 单晶硅 吸收波前模型 强激光损伤 impurity defect optical materials monocrystalline silicon absorption front model laser induced damage 强激光与粒子束
2023, 35(7): 071004
1 天津城建大学理学院, 天津 300384
2 中电科能源有限公司, 天津 300381
3 河北工业大学材料科学与工程学院, 电工装备可靠性与智能化国家重点实验室, 天津 300130
本文研究了铪铁双掺铌酸锂(LN∶Fe, Hf)晶体的衍射效率随光栅写入角度的变化曲线, 并对该关系曲线进行了拟合分析, 发现超阈值的铪铁双掺铌酸锂晶体的体光生伏打系数κ值相比于单掺铁铌酸锂晶体大幅增加。造成κ值变化的原因可能是由于铪离子的掺入消除了晶体中存在的本征缺陷, 而晶格环境的完美化使得留在锂位的铁离子的光生伏打系数大幅上升。此外, 实验结果还表明超阈值的铪铁双掺铌酸锂晶体中参与光折变的缺陷中心浓度约为14.5 ppm (1 ppm=10-6), 即约有4.8%的铁离子仍然“残存”在锂位中, 而这些铁离子可以引起足够强的光折变效应, 成为主导铌酸锂晶体光折变性能的缺陷中心。此外, 还从杂质缺陷-氢氧根基团角度讨论了铁离子晶格占位的可能性。
铌酸锂 光折变 杂质缺陷 缺陷基团 氢氧根振动 本征缺陷 lithium niobate photorefraction impurity defect defect complex hydroxyl vibration intrinsic defect
