Intense short laser pulses are an intriguing tool for tailoring surface properties via ultra-fast melting of the surface layer of an irradiated target. Despite extensive studies on the interaction of femto-second laser interaction with matter, the initial steps of the morphological changes are not yet fully understood. Here, we reveal that substantial surface structure changes occur at energy densities far below the melting threshold. By using low-temperature scanning tunneling microscopy we resolve atomic-scale changes, i.e. the creation of nanosized adatom and vacancy clusters. The two cluster types have distinct non-linear fluence-dependencies. A theoretical analysis reveals their creation and motion to be non-thermal in nature. The formation of these atomistic changes, individually resolved here for the first time, recast our understanding of how surfaces respond to low-intensity ultra-short laser illumination. A visualization and control of the initial morphological changes upon laser illumination are not only of fundamental interest, but pave the way for the designing material properties through surface structuring.

强烈的短激光脉冲是一种有趣的工具，可通过超快速熔化照射目标的表面层来定制表面特性。尽管对飞秒激光与物质的相互作用进行了广泛的研究，但尚未完全了解形态变化的初始步骤。在这里，我们揭示了在远低于熔化阈值的能量密度下会发生显着的表面结构变化。通过使用低温扫描隧道显微镜，我们解决了原子尺度的变化，即纳米级吸附原子和空位簇的产生。这两种簇类型具有不同的非线性注量依赖性。理论分析表明它们的产生和运动本质上是非热的。这些原子变化的形成，在这里首次单独解析，重塑我们对表面如何响应低强度超短激光照射的理解。激光照射时初始形态变化的可视化和控制不仅具有根本意义，而且为通过表面结构设计材料特性铺平了道路。