Understanding of laser-material interactions is a scientific evergreen in the fundamental research of physics and optics. We report here that the ultrafast dynamics of the Cu(110) crystal surface is permanently captured by the formation of subwavelength periodic structures using two collinear femtosecond laser irradiations with different linear polarizations. Surprisingly, such periodic structures are found to have slantwise orientation that is anomalously change as a function of the time delay between two laser beams. In the case of the shorter time delays, the time-dependent slantwise orientations oscillated with terahertz frequency, depending on the pulse width and the intersection angle of two polarization directions, whereas it only presents monotonic change for the larger time delays. Analyses suggests that the former case is attributed to the surface plasmon excitation of the temporally delayed femtosecond laser irradiation on the transient state of the metal surface, which is consequently modulated by some nonthermal effects such as shock wave and bond hardening, while the latter situation is predominated by thermal relaxation of the material lattice. The simulation results agree with the experimental measurements. This investigation not only allows us to sensitively record the transient spatiotemporal evolution on superheated metal surfaces, but also provides insights for the control of material microprocessing.

中文翻译：

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飞秒等离子体激元激发在金属表面瞬态非平衡态下的捕获

在物理和光学基础研究中，对激光与材料相互作用的理解是科学常青。我们在这里报告通过使用不同线性偏振的两个共线飞秒激光辐照形成亚波长周期结构，永久捕获了Cu（110）晶体表面的超快动力学。出人意料的是，发现这种周期性结构具有倾斜取向，该倾斜取向根据两个激光束之间的时间延迟而异常改变。在较短的时间延迟的情况下，随时间变化的倾斜方向以太赫兹频率振荡，具体取决于脉冲宽度和两个偏振方向的交角，而对于较大的时间延迟仅呈现单调变化。分析表明，前一种情况归因于金属表面瞬态上的时间延迟飞秒激光辐照的表面等离子体激元激发，因此，其受到一些非热效应（例如冲击波和键硬化）的调节，而后一种情况是主要由材料晶格的热松弛引起。仿真结果与实验结果吻合。这项研究不仅使我们能够敏感地记录过热金属表面上的瞬时时空演变，而且还为控制材料微处理提供了见识。因此，它受到一些非热效应（例如冲击波和粘结硬化）的调节，而后一种情况则主要由材料晶格的热松弛引起。仿真结果与实验结果吻合。这项研究不仅使我们能够敏感地记录过热金属表面上的瞬时时空演变，而且还为控制材料微处理提供了见识。因此，它受到一些非热效应（例如冲击波和粘结硬化）的调节，而后一种情况则主要由材料晶格的热松弛引起。仿真结果与实验结果吻合。这项研究不仅使我们能够敏感地记录过热金属表面上的瞬时时空演变，而且还为控制材料微处理提供了见识。