摘 要

自梅曼等人制成第一台红宝石激光器以来，人们逐渐且深入地向着短脉冲激光方向做了很多研究，而超短脉冲激光，一直是近些年研究的热点话题。超短脉冲激光加工在微机械加工领域得到了广泛的讨论和应用，特别是在硬脆材料的精密加工领域，而飞秒激光是目前实验室能够获得的最短脉冲激光，能够实现微尺度精细加工，且具有传统长脉冲激光无可比拟的优势，在医学成像、空间测距、眼科、太赫兹光谱学、材料微加工等领域发挥着不可替代的作用，它不仅是人们探索世界的重要工具，也是激光技术的支柱领域。本文主要研究了飞秒激光诱导Cu金属表面微纳结构的作用机理，并对激光工艺参量对其形成的影响规律进行总结，最后对加工表面的功能性应用进行了阐释，拓展了其应用潜力。

1）在传统一维双温模型（Two-Temperature Model）的基础上，结合Drude模型对表面反射率、折射率等光学参数进行了修正，建立了TTM-Drude模型，利用该模型可以较好的对飞秒激光与靶材相互作用过程中电子温度及晶格温度进行瞬态模拟，对激光烧蚀过程中表面热力学参数的变化提供了理论分析基础。

2）系统地分析了飞秒激光工艺参量对表面热力学参数的影响，进而分析了对烧蚀过程及表面形貌的影响规律。结果表明：当脉冲延时小于晶格弛豫时间时，脉冲数的增加可显著提高电子及晶格温度变化的剧烈程度，而当脉冲延时远大于弛豫时间时，电-声耦合已经完成，此时将不会再出现叠加效应；激光能流密度主要决定表面动态热参数的变化程度，进而影响烧蚀机制和烧蚀深度。当其高于某一阈值时，晶格温度超过了Cu金属热力学临界温度，材料将以相爆炸的方式实现去除过程，这是激光烧蚀的主要方式；脉宽会影响电子-晶格系统达到动态热平衡的时间，从而影响激光与靶材相互作用的时间，进而对电子-晶格热影响区域和加工范围造成影响，而波长在模型适用范围内影响相对较小，可作为表面结构微调参数。

3）研究了飞秒激光诱导的表面微纳结构在亲疏水性、光折射性及生物表面相容性等方面的应用，阐释了其作用机理，并结合本文研究成果对获得目标功能性表面的激光参数设置给出了合理的建议。

关键词：飞秒激光；Cu金属；微纳结构；TTM-Drude；功能性应用

Abstract

Since the first ruby laser was made by Maiman et al, the exploration of laser has been widely concerned by scholars, especially the ultrashort pulse laser has been researched as a hot topic in recent years. Ultrashort pulse laser processing has been discussed and applied widely in the field of micromachining, especially the precision machining of hard and brittle materials. Femtosecond laser is the shortest pulse laser available in the laboratory at present, which can achieve microscale fine processing. The advantages of femtosecond lasers have been reported and are considered unmatched by traditional long pulse lasers. At present, femtosecond laser has been widely used and plays an irreplaceable role in medical imaging, space ranging, ophthalmology, terahertz spectroscopy and material micromachining. It is not only an important tool for people to explore the world, but also the pillar field of laser technology. In this study, the mechanism of femtosecond laser-induced micro-nano structure on the Cu metal surface and the influence of laser process parameters on its formation were investigated numerically. In addition, the functional application of the processed surface was explained and its application potential was expanded.

1. Based on the traditional Two-Temperature Model and combined with the Drude model to modify the surface reflectance, refractive index and other optical parameters, the TTM-Drude model was established. It can be used to perform a transient simulation of the electron temperature and lattice temperature during the interaction between the femtosecond laser and the target, and the theoretical analysis basis for the change of the surface thermodynamic parameters during the laser ablation process was provided.

2. The influence of the femtosecond laser parameters on the surface thermodynamic parameters was analyzed systematically, and the influence rules on the ablation process and surface morphology were studied. The results show that when the pulse delay is less than the lattice relaxation time, as the number of pulses increases, the electron and lattice temperatures are significantly increased. However, when the pulse delay is much greater than it, the electro-acoustic coupling has been completed. At this time, the superposition effect will not appear again. The laser energy density mainly affects the peak temperature of the electrons and the lattice, which in turn affects the ablation mechanism and ablation depth. When the energy flow density reaches a certain threshold, the lattice temperature exceeds the Cu metal thermodynamic critical temperature, the material will be removed by phase explosion, which is the main method of laser ablation. Pulse width will affects the electron-lattice system to achieve dynamic thermal equilibrium time, which affects the time the laser interacts with the target, and in turn decides the electron-lattice heat affected area and the processing range. At last, the wavelength has a relatively small effect in the model's applicable range, which can be used as a fine-tuning parameter for the surface structure.

3. The applications of femtosecond laser-induced surface micro-nano structures in the areas of hydrophilicity, light refraction and biological surface compatibility were studied, and its mechanism of action was explained. Combined with the research results of this paper, reasonable suggestions were given for obtaining the laser parameter settings of the target functional surface.

Keywords: femtosecond laser; Cu metal; micro-nano structure; TTM-Drude; functional application

目 录

第1章 绪论 1

1.1 研究背景及意义 1

1.1.1 飞秒激光技术特点 1

1.1.2 飞秒激光与材料相互作用机理及特征 2

1.2 飞秒激光诱导金属表面微纳结构研究进展 3

1.2.1 国外研究现状 3

1.2.2 国内研究进展 4

1.3 本论文主要研究内容 5

第2章 飞秒激光辐照Cu表面理论模型与仿真研究 6

2.1 COMSOL Multiphysics 简介 6

2.2 理论计算模型的建立 6

2.2.1 双温模型（TTM） 6

2.2.2 光学模型 8

2.2.3 烧蚀模型 9

2.3 仿真结果与分析 11

2.4 本章小结 15

第3章 激光工艺参量对微纳结构形成的影响规律研究 16

3.1 脉冲数及脉冲延时 16

3.2 激光能量密度 20

3.3 脉冲宽度及波长 23

3.4 本章小结 26

第4章 微纳结构在功能性方向的应用 28

4.1 亲疏水性 28

4.2 光折射性 29

4.3 表面生物相容性 31

4.3.1 抗菌性能 31

4.3.2 细胞行为 32

4.4 本章小结 33

第5章 总结与展望 34

5.1 论文工作总结 34

5.2 工作展望 35

参考文献 36

致谢 40

第1章 绪论

1.1 研究背景及意义

激光被认为是上世纪最具代表性的突破之一，在社会发展及时代进步的需求下，超短激光微加工已成为最高效、最方便的表面改性技术之一，可为目标提供多种特定需求的一次性解决方案，具有高分辨率、精密加工、没有熔融或重铸层以及单步非接触式工艺等特点，是传统长脉冲激光无可比拟的优势，为精密微纳加工领域开辟了新的可能性，是目前为止微纳加工和高精度材料处理领域最为简单高效的方法之一^[1]。

飞秒激光已成为精密加工领域超短脉冲激光的代名词，具有高效清洁的加工特征，使许多不可能成为可能。此外，它允许人们能够在电子的层面上观察到物质的微观超快运动，对我们了解和认识一些科学现象及理论提供了诸多帮助^[2]。当飞秒激光的辐照强度接近材料阈值附近时，功能性表面微纳结构会通过烧蚀作用产生，研究发现，表面形貌对材料表面的光学性能^[3]、润湿性能^[4]、摩擦性能^[5]及生物相容性^[6]等表面特性具有重要影响，因此研究材料表面的微观形貌对扩展材料的应用潜力具有重要意义，近些年来受到了国内外学者的广泛关注。

目前，飞秒激光表面微纳结构制备已经为生物医疗、航空航天、工业制造、新材料等领域注入了新的活力^[7,8]，激光诱导材料表面微纳结构的研究，为快速制作功能性微纳结构表面器件提供了实验基础，针对飞秒激光诱导材料表面微纳结构的研究具有重要的科学意义和应用价值^[9,10]，利用飞秒激光处理金属^[11,12]、半导体^[13,14]及电介质^[15]以达到其表面改性^[16]目的，是目前广泛研究的热点课题。

1.1.1 飞秒激光技术特点

飞秒（fs）即一千万亿分之一秒，即使是光，在飞秒尺度内也只能用纳米来度量位移。激光在经过了ms、ps、ns等发展阶段之后，飞秒激光目前是在各生产及应用领域中使用最广泛的超短脉冲激光，而在实验室研究领域的探索中，人们正在向阿秒级脉冲激光迈进。飞秒激光脉冲辐照固体靶开辟了激光加工的新途径，成功地应用于许多领域，它具有较强的非线性光学效应，这是它区别于其他工业加工脉冲激光的显著特点，在接触超短脉冲的情况下，激光能量转换为热的特征时间比脉冲持续时间长，热过程发生在激光脉冲通过后，此时，材料烧蚀的机制会有所不同。因此，飞秒激光可以将几乎全部能量沉积在靶材目标区域，而不会出现传统长脉冲激光加工时产生的热影响区，进而实现独特的加工效果。飞秒激光微加工具有如下特点：