Gallais Laurent, Cheng Xinbin, Wang Zhanshan
Opt Lett. 2014 Mar 15;39(6):1545-8. doi: 10.1364/OL.39.001545.
The influence of nodular coating defects on the sub-picosecond laser damage resistance of multilayer coatings is investigated. The study is conducted on engineered nodules from monodisperse silica microspheres in HfO2/SiO2 high-reflective mirrors, at 400 fs/1030 nm. We demonstrate through an experimental study coupled with 3D finite-difference time-domain simulations that nodules in dielectric multilayer coatings are a main concern for the damage resistance of femtosecond optics. The nodules, and hence possibly other defects that produce E-field enhancement in coating materials, induce damage initiation at very low fluences (0.1 J/cm2 in the case under study) compared to the intrinsic damage threshold of the component (1.4 J/cm2 for the present mirror). After initiation, the damage sites grow catastrophically at a determined threshold, reducing significantly the damage resistance (0.6 J/cm2) but allowing a "safe" operating fluence to be defined.
研究了结节状涂层缺陷对多层涂层亚皮秒激光损伤抗性的影响。该研究针对HfO2/SiO2高反射镜中由单分散二氧化硅微球制成的工程化结节进行，波长为400 fs/1030 nm。我们通过结合三维时域有限差分模拟的实验研究表明，介电多层涂层中的结节是飞秒光学元件抗损伤性的主要关注点。与部件的固有损伤阈值（本研究中的镜子为1.4 J/cm2）相比，这些结节以及涂层材料中可能产生电场增强的其他缺陷，会在非常低的能量密度（本研究案例中为0.1 J/cm2）下引发损伤。损伤起始后，损伤部位在确定的阈值下会灾难性地扩展，显著降低抗损伤性（降至0.6 J/cm2），但也能定义出一个“安全”的工作能量密度。
