基于电子激发/电离调控的飞秒脉冲序列宽禁带材料微孔加工

The micro-hole structures in wide bandgap materials are key components in fields like energy, national defense, biology and so on. Femtosecond laser has been used for the fabrication of micro-holes in wide bandgap materials mainly due to its ultra-short pulse duration and ultra-high peak energy. However, the average power of femtosecond pulse is rather low, which leads to low drilling efficiency. Meanwhile, the demands for drilling quality and super diffraction limit feature size of micro-holes in industrial applications get higher and higher. All of above challenge the technology of femtosecond laser hole-drilling. Due to the ultra-short pulse duration of femtosecond laser which is shorter than most characteristic time of physical or chemical processes, the key point of high-efficiency and high-quality hole-drilling is to control the electron excitation/ionization process during the interaction between femtosecond laser and wide bandgap materials. The control of electron excitation/ionization by femtosecond laser pulse trains being the original methodology, this project is aiming at: (1) lucubrating the electron excitation/ionization process within wide bandgap materials under femtosecond laser pulse trains; (2) establishing models of temporally evolutional energy coupling and electron excitation/ionization during the formation of micro-holes, and investigating the transient localized properties change and the microscopic phase change mechanism; (3) researching the controllability of electron excitation/ionization under femtosecond laser pulse trains systematically and revealing its influence on micro-hole fabrication process and results in order to establish the theoretical foundation of a novel method of high-efficiency and high-quality hole drilling in wide bandgap materials.

宽禁带材料微孔是能源、国防、生物等领域核心部件。飞秒激光以其脉冲时间超短，峰值功率超高等优势已在宽禁带材料微孔加工中获得了一定的应用。然而，飞秒脉冲能量小，加工效率较低；同时工业生产及应用中对微孔加工质量、极限尺寸等要求不断提高，对其工艺提出新的挑战。飞秒激光脉宽短于多数物理化学过程特征时间，高效率高品质微孔加工的关键在于调控飞秒激光与宽禁带材料相互作用中电子激发/电离过程。本项目以飞秒激光脉冲序列调控电子激发/电离为手段，深入研究宽禁带材料在飞秒激光脉冲序列作用下的电子激发/电离过程；建立微孔形成过程中脉冲序列及宽禁带材料参数下时域演化的能量耦合及电子激发/电离模型，研究其对后续宽禁带材料瞬时局部特性及相变微观机理；系统研究飞秒激光脉冲序列各个参数对电子激发/电离的可控性，揭示其对微孔加工过程及其结果的影响机理，为形成一种面向宽禁带材料高效率高质量微孔加工新方法奠定理论基础。

超快激光在能量密度、作用空间、时间尺度和被加工材料吸收能量的可控尺度（～电子层面）等方面都分别趋于极端，高效率/高深径比/高品质微纳加工的关键在于调控超快激光与材料相互作用中电子激发/电离过程。本项目以时间（例如脉冲序列）空间（例如贝塞尔光束）整形超快激光调控电子激发/电离为创新研究手段，主要研究成果包括：（1）大幅提高了微孔加工的深径比、质量和大面积一致性，例如空间光场整形调节局部瞬时电子密度分布将微孔深径比提高到330:1（直径1.6微米）、搭建时间分辨观测系统探索了微孔弯曲机理并有效消除微孔弯曲现象从而大幅提高微孔质量、利用飞行时间扫描方法高效率（仅42分钟）加工大面积（1平方厘米）高深径比（330:1）微孔阵列结构结构；（2）利用超快激光时空整形实现了硅表面微纳结构几何形貌调控。例如单脉冲硅表面烧蚀弹坑几何形貌呈现椭圆形貌、少脉冲硅表面诱导出“十字型”周期性微纳结构、脉冲序列硅表面周期性结构呈现各向异性形态，同时基于材料的晶向或加入辅助微结构也可有效实现了表面周期性纹理结构形态与排布的同步调控；（3）基于时空整形的超快激光调控方法提高加工精度及质量，实现超衍射极限加工。通过超快激光空间相位整形调控瞬时局部电子密度，从而调控激光与金属薄膜材料相互作用过程，实现了局部可控的纳米级材料去除，实现高分辨率（约波长的1/14）、高电导率（达体材料的1/4）、任意形状突破衍射极限的金属纳米线结构制备。在本项目支持下，共发表SCI论文13篇，EI论文3篇；申请国家发明专利9项，其中授权3项。在国家学术会议上做特邀报告2次。获得了国家自然科学二等奖1项（排名第5）、教育部自然科学一等奖1项（排名第4），培养的学生（夏博）获得了上银优秀博士学位论文银奖（30万元、全国二名之一）。