The authors report on the theoretical and experimental studies of laser-induced optical breakdown on the surface of fused silica to elucidate the influence of time delay and spatial separation between two ultrashort pulses on the position and size of the modification. Carriers involved in the damage formation including free electrons in the conduction band and self-trapped excitons (STEs) are investigated. The relationship between damage morphology and time delay shows that the seeding carriers (free electrons and STEs) generated from the first pulse are found to play a significant role for the second pulse—which is temporally and spatially separated from the first pulse—in creating the critical electron density needed for an optical breakdown. Consequently, processing outcomes, such as accuracy (position of the hole) and resolution (size of the hole), depend on the interplay of various laser-induced physics that can be tailored for specific goals. As a demonstration, laser lithography with resolution below the diffraction limit is achieved by exploiting multipulse induced physics. This work is a step toward repeatable laser processing of dielectrics beyond the diffraction limit and provides insights into ultrafast laser-matter interaction under the condition of an extremely high pulse repetition rate.

中文翻译：

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使用时空调谐超短脉冲对电介质进行激光加工

作者报告了熔融石英表面激光诱导光学击穿的理论和实验研究，以阐明两个超短脉冲之间的时间延迟和空间分离对修饰位置和大小的影响。研究了参与损伤形成的载流子，包括导带中的自由电子和自陷激子 (STE)。损伤形态和时间延迟之间的关系表明，发现从第一个脉冲产生的种子载流子（自由电子和 STE）对第二个脉冲（与第一个脉冲在时间和空间上分开）起着重要作用。光击穿所需的临界电子密度。因此，处理结果，例如精度（孔的位置）和分辨率（孔的大小）取决于可以针对特定目标量身定制的各种激光诱导物理的相互作用。作为演示，分辨率低于衍射极限的激光光刻是通过利用多脉冲诱导物理实现的。这项工作是朝着超越衍射极限的电介质可重复激光加工迈出的一步，并提供了在极高脉冲重复率条件下对超快激光-物质相互作用的见解。