多重分形谱研究溶胶-凝胶SiO_2疏水减反膜的激光预处理作用

Study of multi-fractal spectrum of sol-gel hydrophobic anti-reflective SiO_2 coating after laser-conditioning

采用溶胶-凝胶提拉技术制备了SiO2疏水减反膜.使用Nd:YAG激光(波长为1064nm,脉宽为7.5ns)采用“Ron1”方式对所得膜层进行了激光预处理.在预处理前后采用“1on1”方式考察了薄膜的激光损伤阈值的变化,使用原子力显微镜(AFM)观察了薄膜的表面形貌的变化,并使用多重分形谱(MFS)方法分析了薄膜分形结构的变化.结果表明经过激光预处理后薄膜的抗激光损伤阈值有了明显提高,均方根表面粗糙度(Rq)稍有减小,膜面变平整,多重分形谱宽度收缩,分形区间的分布均匀性改善.这说明经过激光预处理后薄膜表面微结构趋向规整,使之能够承受更强的激光的辐照.同时也说明借助多重分形谱可以获得更多薄膜表面结构变化的信息,多重分形谱是探索强激光对光学薄膜辐照作用机理的一个十分有用的方法.

Hydrophobic AR SiO2 coating was deposited on the K9 substrate with sol-gel dipping technique, and laser-conditioning was done in ＂R on 1＂ mode with Nd：YAG laser （1064 nm,7.5 ns）. Laser-induced damage thresholds （LIDT） were measured by ＂1 on 1＂ mode, and fore-and-aft changes of the surface morphology and fractal structure of the coating caused by laser conditioning were investigated with atomic force microscope （AFM） and multi-fractal spectrum （MFS）, respectively. The results showed that after laser-conditioning the LIDT of the coating increased obviously, the mean-square roughness decreaseds lightly and the surface of the coating became more smooth, and that width of MFS shrinked and the uniformity of distribution of fractal framework was improved. It means that the micro-structure of the surface of the coating become, so regular that the coating could resist more powerful laser irradiation. Further more, MFS is an effective method to research mechanism of high power laser irradiation on optical coating because we can acquire more information about the change of the surface structure of the coating.