为了研究飞秒激光与铌酸锂表面作用过程中热效应对其表面的影响, 采用重复频率为25MHz、脉宽为100fs、平均输出功率为500mW的紧聚焦飞秒激光对铌酸锂表面进行刻蚀。通过建立热扩散理论模型, 模拟重复频率25MHz的飞秒激光在刻蚀点的温度场分布, 并通过电子显微镜对刻蚀点的形貌进行分析, 发现刻蚀点从内至外形成了3种大小不同、排列疏密不同的颗粒状结构区域, 且中心区域被高温烧蚀并伴有裂缝产生。通过能量色散谱仪对刻蚀点的3种不同结构区域中Nb和O元素的相对含量进行测量, 结合刻蚀点的温度场分布、形貌和元素含量进行了分析。结果表明,Nb和O元素在温度场的驱动下向外扩散; 两者的相对含量对刻蚀点的表面结构具有极大影响。这一结果对高重频飞秒激光刻蚀铌酸锂物理机制及应用的研究是有帮助的。

In order to study thermal effect of femtosecond laser on the surface of LiNbO3 crystal, LiNbO3 crystal surface was etched by tightly-focused femtosecond laser pulses with repetition rate of 25MHz, pulse duration of 100fs and average output power of 500mW. A theoretical thermal diffusion model was built to simulate the temperature filed distribution of the area etched by laser pulses with repetition rate of 25MHz, and the morphology of the etched area was analyzed by a scanning electron microscope. There were three regions with different sizes and densities from the inside to the outside of the etched area, and the central region was ablated by high temperature and was accompanied with the appearance of cracks. Relative contents of Nb and O at the three regions were measured by using energy dispersive spectroscopy and were analyzed with temperature field distribution and morphology. The result shows that Nb and O elements spread out under the drive of temperature field, and relative contents of Nb and O have an important influence on surface structure of etch area. The results are useful for mechanism research of the interaction between high repetition rate femtosecond laser and LiNbO3 crystal.