激光薄膜元件内微缺陷的表征分析  

Characterization Analysis of Micro-Defects in Thin-Film Components for Laser Systems

作　　者：崔云[1,2] 张革 赵元安[1,2] 邵宇川[1,2] 朱美萍[1,2] 易葵[1,2] 邵建达[1,2] Cui Yun;Zhang Ge;Zhao Yuanan;Shao Yuchuan;Zhu Meiping;Yi Kui;Shao Jianda(Laboratory of Thin Film Optics,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China;Key Laboratory of Materials for High Power Laser,Chinese Academy of Sciences,Shanghai 201800,China)

机构地区：[1]中国科学院上海光学精密机械研究所薄膜光学实验室,上海201800 [2]中国科学院强激光材料重点实验室,上海201800

出　　处：《中国激光》2023年第2期50-56,共7页Chinese Journal of Lasers

基　　金：国家自然科学基金(61975215)。

摘　　要：激光系统用薄膜元件既要有优异的光学性能,又要有高的激光诱导损伤阈值(LIDT)。薄膜元件的基底表面上交替沉积有高低折射率材料,通过膜厚、折射率等参数的优化可实现所需的光学性能,但元件中存在的微缺陷(如膜料喷溅缺陷、基底缺陷等)是导致LIDT降低的重要原因。通过精准定位切割、三维重构的方法,表征膜料喷溅和基底抛光产生的微缺陷的形貌结构,并对其激光辐照前后的元素分布进行了分析。研究结果为镀制工艺、基底加工工艺的改进提供了参考。Objective Thin-film components of laser systems require excellent optical performance and a high laser-induced damage threshold(LIDT).The micro-defects in the components(such as coating material ejection defects and substrate defects)are the critical cause for the reduced LIDT.To control micro-defects,we must first detect the defects and trace the formation process of micro-defects.In this study,the morphologies and structures of the micro-defects produced by coating and substrate polishing are characterized by precise cutting and three-dimensional reconstruction.Additionally,the element distributions before and after laser irradiation are analyzed.The results clarify the direction of the increasing LIDT of thin-film components.Methods High-reflection films at 355 nm and 532 nm are deposited on BK7 substrates using the electron beam evaporation.The BK7 substrates are also used for surface topography measurements and additional measurements.Before deposition,the coating chamber is heated to 473 K and evacuated to a base pressure of 1×10~(-3) Pa.The deposition rates of HfO_2 and SiO_2 in the multilayer coatings are 0.1 nm/s and 0.2 nm/s,respectively.H and L represent the HfO_2 and SiO_2 layers with a quarter-wavelength optical thickness(QWOT) at 355 nm or 532 nm,respectively(Fig.1).The morphologies of the micro-defects are observed using focused ion beam scanning electron microscopy(FIB-SEM).The feature points are cut with an ion beam to obtain the cross-sectional morphology and structure,and the element composition in the designated area is analyzed using an energy dispersive spectrometer(EDS).Scanning transmission electron microscopy-high angle annular dark field(STEM-HAADF) images of the micro-defects are obtained using a 200keV field emission transmission electron microscope(TEM).Three-dimensional reconstruction is conducted to analyze the submicron defects.Samples are prepared for the TEM observations using FIB-SEM.The LIDT is tested by 1-on-1.A 2ωNd:YAG laser with a pulse width of 8 ns and a 3ωNd:YAG laser

关 键 词：薄膜 激光损伤 微缺陷 喷溅 基底抛光 

分 类 号：O439[机械工程—光学工程]