PVP掺杂-ZrO2溶胶-凝胶工艺制备多层激光高反射膜的研究

以丙醇锆(ZrPr)为锆源，二乙醇胺(DEA)为络合剂，原位引入聚乙烯吡咯烷酮(PVP)，在乙醇体系中成功地合成了PVP掺杂-ZrO₂溶胶.采用旋涂法在K9玻璃基片上制备了PVP-ZrO₂单层杂化薄膜.用不同掺杂量的PVP-ZrO₂高折射率膜层与相同的SiO₂低折射率膜层交替沉积四分之一波堆高反射膜.借助小角X射线散射研究胶体微结构，用红外光谱、原子力显微镜、紫外/可见/近红外透射光谱、椭圆偏振仪以及1064nm的强激光辐照实验对薄膜的结构、光学和抗激光损伤性能进行表征.研究发现，体系组成的适当配置可以在溶胶稳定的前提下实现ZrPr的充分水解，赋予薄膜良好的结构、光学和抗激光损伤性能.杂化体系中，DEA与ZPr之间强的配合作用大大降低了ZrO₂颗粒表面羟基的活性，使得PVP大分子只是以微弱的氢键与颗粒的表面羟基作用而均匀分散于ZrO₂颗粒的周围，对颗粒的形成和生长无显著影响.因而在实验研究范围内，随PVP含量的增大，PVP-ZrO₂杂化膜层的折射率和激光损伤阈值均无显著变化.但是，薄膜中均匀分布的PVP柔性链可以有效促进膜层应力松弛，显著削弱不同膜层之间的应力不匹配程度、大大方便多层光学薄膜的制备.当高折射率膜层中PVP的质量分数达到15%—20%时，膜层之间良好的应力匹配使得多层高反射膜的沉积周期数可达到10以上.沉积10个周期的多层反射膜，在中心波长1064nm处透射率约为1.6%—2.1%，接近全反射特征，其激光损伤阈值为16.4—18.2J/cm²(脉冲宽度为1ns). 关键词： 溶胶-凝胶 2')" href="#">PVP-ZrO₂ 高反射膜 激光损伤

Sol-gel deposition of highly reflective multilayer coatings from PVP-ZrO2 hybrid systems

A series of ZrO₂ and polyvinylpyrrolidone (PVP) doped-ZrO₂ sols have been synthesized by the controlled hydrolysis and condensation of zirconium n-propoxide, with diethanolamine (DEA) as the chelating agent. PVP-ZrO₂ hybrid monolayers and highly reflective (HR) multilayer coatings were then prepared by spin-coating the stable sols on K9 glass substrates. The fabrication of the HR coatings involves alternate depositions of PVP-ZrO₂ (as the high-index material) and SiO₂ (as the low-index material) layers. The microstructures of the sols, the structural and optical properties, as well as the laser damage resistance of the films were thoroughly characterized. By virtue of the small angle X-ray scattering (SAXS) analysis, the sol-gel processing parameters were successfully optimized, endowing the as-prepared films with good optical properties and high laser damage resistance. SAXS studies also offer the possibility to a good knowledge of the microstructure of the sols. In our hybrid system, the unhydrolyzed DEA ligands, which become anchored in the inorganic network, may considerably weaken the effects of PVP on the formation and growth of ZrO₂ particles. Hence, the incorporation of a proper amount of PVP gives rise to negligible change of the sol structure and only a slight variation in refractive index and laser damage resistance of the films. However, at the slight expense of the refractive index and laser damage resistance, the incorporation of PVP can easily alleviate the stress incompatibility between different layers and facilitate the fabrication of the multilayer coatings. As the mass fraction of PVP reaches 15%—20%, a perfect match between different layers can be achieved, which ensures the successful deposition of 21-layer, nearly full-reflection coatings with the minimum transmittance of about 1.6%—2.1% (at 1064nm) and high laser damage threshold of 16.4—18.2J/cm² (at 1064nm, 1ns pulse duration and R/1 mode).