针对参量振荡过程中铌酸锂表面的增透薄膜的损伤问题, 采用了XRD光谱法和形貌观测法对激光诱导薄膜损伤的形貌及其物理过程进行了深入地分析. 观测发现： 薄膜损伤点的特征是膜面出现凹陷的点坑, 周围分散着由厚到薄变化的沉积层, XRD光谱检测显示出现了薄膜材料的晶化. 利用杂质缺陷诱导薄膜损伤模型对以上损伤的形貌成因进行了分析. 研究表明： 杂质粒子对激光脉冲能量的强烈吸收会引起邻近光学材料的迅速熔化、 汽化和电离, 形成复杂物态结构混合物; 在激光等离子体冲击波作用下, 混合物发生喷溅扩散形成凹陷坑. 在扩散冷却过程中沉积物会发生结晶, X射线衍射显示出薄膜材料SiO2晶态的衍射峰.

In an attempt to elucidate the damage in high transmission thin films on LiNbO3 crystal in optical parametric oscillator, the authors employed XRD spectrometry to investigate the spectrum of laser-induced damage in thin film as well as the morphology of the damage. The authors observed that the damage of thin film was characterized by the depressions/craters in the surface of the films, which were surrounded by a deposition layer with the deceasing thickness from the center of the craters. The XRD measurements indicate that the film was crystallized. The authors analyzed the causes of morphologies and the mechanism of crystallization with the aid of the model for impurity-induced damage in thin solid films. The crystallization was due to the solidification of liquid and gaseous mixtures that result from the strong absorbing to the incident laser. The crater was generated because the mixtures were ejected under the extensive pressure of the laser plasma shock wave. During the process that the mixtures deposit around the craters, the density of the mixtures will decrease and crystallization takes place. As a result, the color of the deposition layer becomes lighter from inside to outside, and the crystallization of the thin film materials was observed by XRD spectrometry.