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研究了超短脉冲激光照射下LiF晶体的破坏机理及其超快动力学过程,利用扫描电镜和原子力显微镜等测试手段,观测了飞秒激光照射下LiF晶体的烧蚀形貌。利用烧蚀面积与激光脉冲能量的对数关系确定了LiF晶体的破坏阈值,并利用非线性玻璃棒展宽脉宽,得到了800 nm激光作用下LiF破坏阈值对激光脉宽(50~1000 fs)的依赖关系;利用抽运探针超快探测平台,探测了LiF烧蚀过程中反射率的变化。采用雪崩击穿模型,并根据晶体材料反射率与材料的介电常量的依赖关系,通过数值计算,模拟了材料烧蚀阈值与脉宽的依赖关系及材料激发过程中反射率的变化关系。结果表明,理论结果与实验结果符合较好。讨论了飞秒激光照射下LiF晶体中导带电子数密度的变化规律,并解释了相应的实验结果。
The failure mechanism and ultrafast kinetics of LiF crystal irradiated by ultrashort pulse laser were studied. The ablation morphology of LiF crystal was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The damage threshold of LiF crystal was determined by the logarithm relationship between ablation area and laser pulse energy, and the damage threshold of LiF crystal under 800 nm laser was obtained. The pulse width (50 ~ 1000 fs) The dependence of reflectivity in the LiF ablation process was exploited by the ultra-fast detection platform of the pumping probe. The avalanche breakdown model is adopted. According to the dependence of the reflectivity of the crystal material and the dielectric constant of the material, the dependence of the threshold and the pulse width of material ablation and the change of reflectivity in the process of material excitation are numerically calculated. The results show that the theoretical results are in good agreement with the experimental results. The variation rule of the number density of conduction band electrons in LiF crystal irradiated by femtosecond laser was discussed and the corresponding experimental results were explained.