Investigating surface damage characteristics in DKDP crystals by laser irradiation at 355 nm and 1064 nm
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摘要: 利用Nd:YAG激光器研究了DKDP晶体元件在激光辐照下的表面损伤特性,对比研究了355 nm和1064 nm激光辐照下晶体元件的表面损伤形貌,分析了每种损伤形貌对应的前驱体和损伤机制。研究结果表明:相对于体损伤,晶体的表面损伤更加复杂,在脉宽约10 ns、损伤概率小于等于50%的激光能量密度辐照下,DKDP晶体的表面损伤主要有带坑底空腔损伤坑、表面损伤裂纹、平底损伤坑、表面烧蚀四种典型形貌。通过光学显微镜和扫描电子显微镜的成像和分析发现:带坑底空腔损伤坑和表面损伤裂纹的前驱体都是晶体体缺陷,平底损伤坑的前驱体则可能是表面加工裂纹、裂纹内碎屑、表层体缺陷等中的一种或多种,表面烧蚀主要由表面污染和浅表层缺陷形成。与熔石英光学元件一样,表面损伤仍然是晶体元件抗激光辐照损伤的薄弱环节。Abstract: The surface damage characteristics in DKDP crystals under laser irradiation at 355 nm and 1064 nm were studied and compared by using a Nd: YAG laser. The damage precursors and mechanisms corresponding to each damage morphologies were analyzed. The damage results reveal that the surface damage in DKDP crystal is more complex than that in bulk damage. Under the irradiation laser corresponding to the pulse width of 10 ns and the damage probability at 0% − 50%, surface damage morphology in DKDP crystals mainly contained four typical damage morphology: crater with cavity, crater with flat bottom, surface damage crack, and surface ablation. Through the comparison and analysis of the imaging of optical microscope and scanning electron microscope, damage precursors that induced damage craters with bottom cavity and surface cracks were mainly bulk defects, which were the same as the precursors forming the internal damage points (pinpoints). The precursors that induced damage craters with flat bottom were relatively complex, which could be the surface contamination, surface cracks, machining defects, and shallow surface bulk defects. For surface ablation, it was mainly caused by surface contamination and surface absorption defects. Surface damage is still one of the important factors limiting the laser damage resistance of KDPD crystals.
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表 1 表面损伤形貌的特征数据
Table 1. Characteristic data of surface damage morphology
depth of damage
crater/μmsize of damage
crater/μmprobability of
occurrence/%damage precursor crater with cavity 15~100 50~300 ~30 crystal bulk defect crater with flat bottom 5~50 50~200 ~60 surface cracks and surface defect surface damage crack 20~100 50~200 ~5 crystal bulk defect surface ablation and others − 30~500 ~5 surface contamination and surface defect -
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