CAREER: Nanolithography Using Ultrashort-Pulsed Laser Processing

这项教师早期职业发展（Career）计划资助了基于激光的先进制造的基础研究，该研究使单步制造纳米级结构成为可能。目前的纳米制造工艺涉及多个步骤，不适合以经济有效的方式制造独一无二或定制的纳米结构。在这个项目中，一种超短脉冲激光，它发出的光（脉冲）的持续时间极短，被用来以纳米级的精度钻孔，切割和图案材料。由于脉冲的持续时间很短（不到万亿分之一秒），激光脉冲的能量高度集中在材料中，创造了其他加工方法通常无法实现的条件。超短脉冲激光加工提供了显著减少附带损伤的关键优势，即破坏周围材料，从而提高了各种材料加工的精度。该项目推进了对超短脉冲激光加工介电材料的理解，如玻璃和金刚石，这些材料通常用于显示面板，微电子和切割工具。该项目取得的进展使纳米尺度图案的新方法得以实现，从而缩短了制造时间，降低了成本，并通过支持旨在培养训练有素的制造业劳动力的教育和推广计划，使社会受益。该项目提高了公众对日常生活中激光和光学技术的认识，吸引了年轻学生对科学和技术的兴趣，并引导大学生追求先进制造业的职业生涯。新的纳米光刻方法基于激光烧蚀，使用一系列超短激光脉冲（脉冲序列），该脉冲序列被暂时调谐以产生自由载流子种群的局部化并增强激光能量的吸收。研究和控制超短激光脉冲与宽禁带介质之间的非线性相互作用，以提高空间分辨率和能量吸收效率。这项研究产生了关键工艺参数和相关纳米尺度物理的知识，使这种新的纳米制造方法成为可能。探索了三种加工模式-钻孔，切割和投影（使用电子控制的空间光调制器作为可定制的掩模），并研究了每种模式特有的挑战。利用瞬态泵浦探针显微技术和激光损伤阈值测量技术研究了介质材料激光加工过程中的时空电子动力学。利用脉冲序列处理与掩模投影光刻相结合的系统，演示了任意纳米结构的大面积图像化。该项目提高了超短脉冲激光器作为制造工具的能力，并为研究损伤阈值以上激光-物质相互作用开辟了新的机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development (CAREER) Program grant supports basic research in laser-based advanced manufacturing that enables single-step fabrication of nano-scale structures over a large area. Current nanofabrication processes involve multiple steps and are not suitable for fabricating one-of-a-kind or customized nanostructures in a cost-effective manner. In this project, an ultrashort-pulsed laser, which emits flashes of light (pulses) with extremely short duration, is used to drill, cut and pattern materials with nano-scale precision. Because the duration of a pulse is so short (less than one trillionth of a second), the energy of the laser pulse is highly concentrated in the material, creating conditions that are not normally achieved with other processing methods. Ultrashort-pulsed laser processing provides the key advantage of significantly-reducing collateral damage, that is damaging the surrounding material, and thus improving precision in the processing of a variety of materials. This project advances the understanding of ultrashort-pulsed laser processing of dielectric materials, such as glass and diamond, which are commonly used in display panels, microelectronics and cutting tools. Advances resulting from the project benefits society by enabling a new method for nano-scale patterning that reduces manufacturing time and lowers cost, and by supporting an education and outreach program aimed at cultivating a well-trained manufacturing workforce. The project raises public awareness of laser and optical technologies in everyday life, attracts young students to science and technology, and guides college students to pursue a career in advanced manufacturing. The new nanolithography method is based on laser ablation using a sequence of ultrashort laser pulses (a pulse train) that is temporally tuned to create localization of free-carrier population and enhanced absorption of laser energy. Nonlinear interaction between ultrashort laser pulses and wide-bandgap dielectrics is studied and controlled to enhance spatial resolution and improve energy-absorption efficiency. The research generates knowledge of the critical process parameters and relevant nanoscale physics that enable this new nanofabrication method. Three processing modes - drilling, cutting, and projection (using an electronically-controlled spatial light modulator as a customizable photomask) - are explored, and the challenges unique to each mode are studied. Spatial and temporal electron dynamics, which play a key role in laser processing of dielectric materials, are investigated by transient pump-probe microscopy and laser damage threshold measurement. Large-area patterning of arbitrary nanostructures are demonstrated using a system that integrates pulse-train processing with mask-projection lithography. This project enhances the capability of ultrashort-pulsed lasers as a manufacturing tool and opens up new opportunities for studying laser-matter interactions in the above-damage-threshold regime.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.