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 ablation mechanism and ultra-fast dynamics property of LiF crystal are studied. By means of SEM and AFM the damage features induced by femtosecond laser are observed. Based on the logarithmic dependence of the ablated area on laser pulse energy, the ablation threshold fluence of LiF crystal is calculated. Meanwhile, stretching the pulse duration up to 800 fs with dispersive material, the threshold fluence of LiF is got as a function of pulse duration. By use of pump-probe technique, the dependence of reflectivity of LiF crystal on delay time is got while irradiated by 800 nm femtosecond laser with 70 fs and 500 fs pulse duration respectively. Then based on the avalanche mode and the relationship between the reflectivity and the dielectric constant, a calculation in theory is made. The theoretical calculation results agree well with the experimental results. Finally the variety of the density of conduction band electrons in the ablation process is discussed and the experimental result with avalanche mode is interpreted.