【摘要】 本文针对不同入射角度设计了系列反射率大于99.5%的薄膜结构，理论分析了设计入射角度对没有节瘤缺陷的理想反射薄膜和有节瘤缺陷的反射薄膜电场分布的影响。采用电子束蒸发在没有预植和预植节瘤缺陷种子的基底上制备了4种不同设计入射角度的反射薄膜，对其纳秒和皮秒激光损伤特性进行了研究。结果表明，反射薄膜内部电场分布与设计入射角度和节瘤种子直径密切相关。随着设计入射角度增加，膜层厚度呈现减小的趋势，理想反射薄膜的内部电场强度降低，设计入射角度下的皮秒激光损伤阈值提升。节瘤缺陷引起膜层内部局部电场增强，导致激光损伤阈值降低。在纳秒激光辐照下，节瘤缺陷引起的初始损伤位于靠近空气的SiO2层中的电场强区；在皮秒激光辐照下，节瘤缺陷引起的初始损伤位于与入射光束方向相对一侧的节瘤边界中部的电场强区。本文研究为不同入射角度的激光反射薄膜和激光系统的光路设计提供了参考。更多还原

【Abstract】 Objective As a critical optical component in laser systems, the performance of high-reflective coatings directly influences the output power of the entire laser system. Particularly in high-power laser applications, the laser-induced damage threshold(LIDT) of these coatings is a key limiting factor. The angle of laser incidence significantly affects the LIDT of coatings. Numerous studies have explored the influence of laser incident angle on temperature distribution, electric field(E-field) distribution, and LIDT of high-reflective coatings. However, most samples are designed for specific incident angles. To enhance performance, it is essential to design coating structures based on practical usage angles. Through systematic theoretical analysis and experimental research, understanding the relationship between high-reflective coatings designed for different angles and their LIDTs can provide valuable insights for designing these coatings and selecting optimal incident angles in laser system configurations.Methods High-reflective coatings(Rs≥99.5% at the center wavelength of 1064 nm) are designed and deposited using electron beam evaporation on substrates, both with and without pre-planted nodule seeds, for different incident angles.The finite element method(FEM) is employed to simulate the E-field distributions of the coatings under their respective design angles and working laser wavelengths, as well as the localized E-field distribution optimized by nodule defects of varying diameters. The nanosecond and picosecond LIDTs of the samples are measured in accordance with ISO 21254standards. The transmittance spectrum of the coatings is measured using a spectrometer(Lambda 1050 UV/VIS/NIR,Perkin-Elmer), and the reflectance spectrum is calculated while neglecting absorption. The surface figure of the coatings is characterized using an optical interferometer(ZYGO Mark Ⅲ-GPI). The root-mean-square(RMS) roughness of the coatings is measured with an atomic force microscope(AFM, Veeco Dimension-3100).Results and Discussions FEM simulation results show that the E-field distribution within the high-reflective coatings closely correlates with the design incident angle and nodule seed diameter(Fig. 2). The peak E-field intensity increases with the design incident angle, and the localized E-field enhancement is more pronounced at nodule defects with larger seed diameters(Fig. 3). Experimental results indicate that the LIDT(1053 nm, 8.6 ps) of the high-reflective coating increases with the design incident angle, partly due to the decrease in peak E-field intensity(Fig. 6). The damage morphology induced by laser irradiation at near-LIDT fluence manifests as isolated pits. As the laser fluence intensifies, so too does the density of damage pits, which eventually results in substantial damaged spots(Fig. 8). For high-reflective coatings deposited on substrates pre-planted with nodule seeds(diameter: 1000 nm), the initial damage closely correlates with the localized E-field enhancement at the nodule defect(Fig. 9). Under laser irradiation with a pulse width of 10 ns, the typical damage morphology includes a nodule-related pit surrounded by plasma scalds. The damage initiation position corresponds to the enhanced E-field distribution of the outermost SiO2 layer at the nodule dome. Under laser irradiation with a pulse width of 8.6 ps, the damage initiation position corresponds to the enhanced E-field distribution of the outermost SiO2 layer at the nodule dome and the middle area of the nodule boundary opposite the laser incident direction(Fig. 11). Further characterization of cross-section damage morphology demonstrates that damage in the middle region of the nodule boundary initiates at lower laser fluence compared to damage at the nodule dome(Fig. 10).Conclusions High-reflective coatings are designed with different laser incident angles. The effects of the design incident angle and nodule defects on the E-field distribution, as well as the laser-induced damage properties of high-reflective coatings, are theoretically and experimentally compared. FEM simulation results show that the E-field distribution closely relates to the design incident angle and the diameter of nodule defect seeds. For a given target reflectivity, high-reflective coatings with larger design incident angles exhibit lower peak E-field intensities. Nodule defects cause localized E-field enhancement, with larger seed diameters leading to more marked enhancements. Experimental results demonstrate that the design incident angle noticeably affects the nanosecond and picosecond LIDTs of high-reflective coatings, and the laser damage morphology correlates closely with the E-field distribution within the coating. In coatings with pre-existing nodule seeds, initial damage induced by nanosecond lasers appears on the outermost SiO2 layer of the nodule dome, while damage induced by picosecond lasers appears at the midpoint boundary of the nodule defect. This research serves as a valuable reference for designing high-power laser coatings and laser systems.更多还原