1064 nm激光对中性密度滤光片的损伤机理研究

中性密度滤光片的典型结构是在K9玻璃上镀金属膜,来实现对激光的有效吸收.由于损伤阈值较低,严重限制了其在高能激光系统中的应用.实验研究了较高激光能量密度下滤光片的损伤形貌和损伤机理.损伤形貌的变化特征是:随着激光能量密度的增加,滤光片先出现损伤点,后以损伤点为中心产生裂纹,且裂纹长度逐渐变长,最终连接成线状和块状,导致大面积的薄膜脱落.建立了缺陷吸收激光能量升温致中性密度滤光片表面薄膜损伤的模型,计算了薄膜表面的温度和应力分布,讨论了薄膜表面不均匀温升造成的径向、环向和轴向热应力分布.理论分析显示:环向应力是造成薄膜沿径向产生裂纹的主要原因.当激光能量密度大于约2.2 J/cm²,杂质粒子半径大于140 nm且相邻杂质粒子之间的距离小于10 μ m时,裂纹才能大量连接起来引起薄膜的大面积脱落.

Investigation of 1064-nm laser damage mechanism of neutral density filter

The typical neutral density filter is a metal film plated on a K9 glass to achieve the effective absorption of laser.Its lower damage threshold severely restricts its application to high energy laser systems.Experimental study on damage morphology and damage mechanism of filter in a higher laser energy density is carried out.The variation characteristics of damage morphology are as follows:with the increase of laser energy density,damage spots first appear on the filter,then develop into cracks,and the cracks grow gradually longer and eventually connect into linear and block forms,resulting in a large area of film dropping off.A model of defect absorption leading to film damage on neutral density filter is established.And temperature and stress distributions on the film surface are calculated,separately.The inhomogeneous temperature rise on film surface leads to radial,hoop and axial thermal stress distributions.Theoretical analysis shows that cracks along the radial direction are caused by hoop stress.When laser energy density is larger than about 2.2 J/cm~2,impurity particle radius is larger than 140 nm and the distance between impurity particles is less than 10μm.A large number of cracks can connect together to cause a large area of film to drop off.