高激发硅中的可饱和吸收及其在表面的抑制
Saturable absorption in highly excited silicon and its suppression at the surface
AI总结：
通过第一性原理计算揭示了激光辐照硅中泡利阻塞导致的可饱和吸收现象，并发现表面因对称性破缺可抑制该效应。
摘要：
通过基于含时密度泛函理论的第一性原理计算，数值研究了有限电子温度下激光辐照硅中的非线性电子激发。在近红外激光辐照下，处于有限温度的体硅中，我们发现即使使用少周期脉冲，在特定激光强度下吸收能量也会达到饱和。尽管在该激光强度下，导带到导带和价带到价带的单光子跃迁过程占主导地位，但泡利阻塞抑制了进一步的单光子跃迁。在更高强度下，跨带隙的多光子激发压倒了单光子激发，可饱和吸收现象消失。在有限温度硅的表面，对称性破缺抑制了泡利阻塞，吸收能量相对于体区域的可饱和吸收能量有所增强。
英文摘要：
Nonlinear electronic excitation in laser-irradiated silicon at finite electron temperatures is numerically investigated by first-principles calculations based on the time-dependent density functional theory. In bulk silicon at finite temperatures under near-infrared laser irradiation, we found that the absorbed energy is saturated when using a certain laser intensity even with a few-cycle pulse. Although one-photon processes of conduction-to-conduction and valence-to-valence transitions are dominant at such a laser intensity, the Pauli blocking inhibits further one-photon transition. With higher intensities, multi-photon excitation across the bandgap overwhelms the one-photon excitation and the saturable absorption disappears. At the surface of finite-temperature silicon, the Pauli blocking is suppressed by the symmetry breaking and the absorbed energy is relatively enhanced from the energy of the saturable absorption in the bulk region.
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