Mechanism of micro-waviness induced KH2PO4 crystal laser damage and the corresponding vibration source

• Published in: 中国物理B：英文版 2012-05, Vol.21 (5), p.34-42
• Main Author: 李明全 陈明君 安晨辉 周炼 程健 肖勇 姜伟
• Format: Article
• Language: English
• Subjects: 微型; 惯性约束聚变; 振动源; 波纹度; 激光损伤阈值; 磷酸二氢钾晶体; 空间频率; 诱导机制
• ISSN: 1674-1056; 2058-3834
• DOI: 10.1088/1674-1056/21/5/050301

The low laser induced damage threshold of the KH2PO4 crystal seriously restricts the output power of inertial confinement fusion.The micro-waviness on the KH2PO4 surface processed by single point diamond turning has a significant influence on the damage threshold.In this paper,the influence of micro-waviness on the damage threshold of the KH2PO4 crystal and the chief sources introducing the micro-waviness are analysed based on the combination of the Fourier modal theory and the power spectrum density method.Research results indicate that among the sub-wavinesses with different characteristic spatial frequencies there exists the most dangerous frequency which greatly reduces the damage threshold,although it may not occupy the largest proportion in the original surface.The experimental damage threshold is basically consistent with the theoretical calculation.For the processing parameters used,the leading frequency of micro-waviness which causes the damage threshold to decrease is between 350-1 μm-1 and 30-1 μm-1,especially between 90-1 μm-1 and 200-1 μm-1.Based on the classification study of the time frequencies of microwaviness,we find that the axial vibration of the spindle is the chief source introducing the micro-waviness,nearly all the leading frequencies are related to the practical spindle frequency（about 6.68 Hz,400 r/min） and a special middle frequency（between 1.029 Hz and 1.143 Hz）.