纳秒激光诱导聚酰亚胺薄膜周期性结构的产生

采用波长为355 nm、脉宽为7 ns、重复频率为1 Hz的线性偏振激光在聚酰亚胺薄膜表面制备了微米量级的周期性表面结构，并讨论了激光参数对条纹形貌的影响。实验发现，周期性结构的产生存在一定的能量密度阈值和脉冲个数阈值，当激光能量密度范围在54~586 mJ/cm2，脉冲个数在1~50时，能在聚合物薄膜表面产生周期为4~6.65 μm的规整条纹结构。在保持激光能量密度不变的情况下，增加脉冲个数，或者保持脉冲个数不变，增大入射到材料表面的激光能量密度，都能引起条纹周期增大，并且根据实验结果，随着脉冲个数的增加，烧蚀坑的深度增加，LIPSS能持续出现在坑底。此外，为分析周期性结构形成的可能原因，通过对热传导模型的建立讨论了当周期性结构形成时材料历经的物理状态。文中的相关研究结果对基于LIPSS实现的材料表面润湿性、摩擦力学、光学特性的改善提供了一定的研究基础。

Nanosecond laser-induced periodic structures on polyimide film

Laser-induced periodic surface structures (LIPSS) were created by a 355 nm linearly polarized laser with the pulse duration of 7 ns and the pulse repetition rate of 1 Hz on polyimide films. The influences of different laser parameters on the morphology of the formed LIPSS were investigated. It is found that there is a certain fluence threshold and pulse number threshold for the generation of periodic structure. When the laser fluence is in the range of 54-586 mJ/cm2, and the pulse number is between 1-50, the well-ordered LIPSS are formed with the periods between 4-6.65 μm. The pulse number and the laser fluence are changed in the experiment. With the same laser fluence, increasing the pulse number, or with the same pulse number, increasing the laser fluence, the period of the ripples can be increased. It is also observed that the formation of LIPSS is accompanied by the removal of materials, with the increase of the pulse number, the depth of the crater increases, and LIPSS can continue to appear at the bottom of the crater. In addition, in order to analyze the possible causes of the formation of periodic structure, the physical state of the material is discussed by establishing the heat conduction model when the periodic structure is formed. These works provide potential support for studying the improvement of material surface wettability, friction mechanics, and optical properties.