Despite recent successes in three-dimensional ultrafast laser writing inside silicon and other narrow gap materials, strong discrepancies remain in the identified narrow experimental windows to exceed material breakdown thresholds. In an experiment in which we irradiate silicon with perfectly synchronized femtosecond, picosecond, and nanosecond pulses, we show that the temporal contrast of the ultrashort pulses is a critical driving parameter, even more than the achievable peak vacuum intensity. We identify by appropriate pulse combinations breakdown channels seeded by pre-ionization and thermal runaway from the simulated contrast imperfections. The introduction of this multi-timescale control of the interactions allows bulk writing inaccessible otherwise. It also permits a comprehensive review of previous reports using infrared laser technologies at different characteristic contrast performances. The quantitative analysis of the problem reveals an extremely high sensitivity with modification ignition at intensity contrasts down to ${10}^{-6}$ and below. This sensitivity level is common for high-intensity physics experiments but has no equivalent in any other laser material processing application.

中文翻译：

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时差瑕疵是块状硅中超快激光修改的驱动力

尽管最近在硅和其他窄间隙材料内部进行三维超快激光写入方面取得了成功，但在已确定的窄实验窗口中仍存在巨大差异，超过了材料击穿阈值。在一个以完全同步的飞秒，皮秒和纳秒脉冲照射硅的实验中，我们证明了超短脉冲的时间对比度是一个关键的驱动参数，甚至超过了可达到的峰值真空强度。我们通过适当的脉冲组合从模拟的对比缺陷中识别出预电离和热失控所产生的击穿通道。这种对交互作用的多时标控制的引入允许批量写入，否则将无法访问。它还允许使用红外激光技术以不同的特性对比性能全面回顾以前的报告。对问题的定量分析显示，在强度对比降低至${10}^{-6}$及以下。此灵敏度水平在高强度物理实验中很常见，但是在任何其他激光材料加工应用中却没有。