KTP晶体的激光烧蚀特性及Raman光谱研究

Study on Characteristics of Laser Ablation in KTP Crystal and Its Influence on the Raman Spectroscopy

高阈值的KTP晶体的研发,对高能激光领域至关重要。采用高重复频率的紫外激光对KTP进行烧蚀,并对烧蚀前后的Raman光谱进行分析,研究发现:激光等离子体效应是造成晶体破坏的主要原因,其逆韧致吸收效应会大大增加激光脉冲能量的沉积,电离效应使得晶体发生充分的离解,高压冲击波效应则把熔化、气化以及电离混合物外排的同时,使得材料发生断裂。烧蚀前后的Raman光谱的特征峰分布基本相同,说明烧蚀作用没有改变KTP材料的整体结构。但是,特征峰的对比值(RIR)都发生了改变,且有所展宽,说明烧蚀后结晶度降低。其中TiO6和PO4等主要氧多面体的特征峰向低波数漂移,说明材料的键合力消弱,更易发生离解。

The research and development of the KTP crystal with high threshold is of very importance for its application in high- energy laser systems. Ablation characteristics in KTP crystal as well as their influence on the Raman spectroscopy were studied by UV laser with high repetition frequency. The research results show that the laser plasma effects are the main reasons for the damage in the KTP crystal. The inverse bremsstrahlung absorption effect can increase the deposition of the laser pulse energy greatly; the ionization effect can make the crystal dislocated completely; shock wave effect can push away the mixture of melted, vaporized and ionized materials and cause cracks in the pit. Through investigation and comparison of the Raman spectroscopy be- fore and after the laser ablation, it was found that the distribution characteristics of Raman peaks are almost the same, sugges- ting that the basic structures of KTP crystal do not change. But almost all the Raman characteristic peaks＇ RIR values have changed and the widths are broadened, which means that the crystalline degree has been decreased. The Raman peaks of TiO6 and PO4 oxygen polyhedron shift to the lower wave number, which indicates that bonding force becomes weaker and the KTP crystal can be damaged easily.