硅中的光电离和瞬态Wannier-Stark阶梯：第一原理模拟与Keldysh理论
Photoionization and transient Wannier-Stark ladder in silicon: First principle simulations versus Keldysh theory
摘要：
非线性光电离的晶体和半导体被广泛处理的框架中的Keldysh理论的有效性是有限的，以小的光子能量相比，带隙和相对较低的激光强度。含时的密度泛函理论（TDDFT）模拟，这是免费的这些限制，使深入了解电子结构的非平衡动力学。在这里，我们应用TDDFT研究硅晶体的光电离超短激光脉冲在宽范围的激光波长和强度，并比较的结果与Keldysh理论的预测。从模拟得到的光电离率大大超过与Keldysh理论的有效范围内，后者获得的数据。可能的原因的差异进行了讨论，我们提供的Keldysh理论的限制之外的光电离率的基本数据。通过研究Stark位移随光子能量和激光场强度的变化特征，揭示了Wannier-Stark梯形瞬态态的一种表现形式，它随激光场强度的增加而变得模糊。最后，它表明，TDDFT模拟可以潜在地提供可靠的数据上的电子阻尼时间，是非常重要的大规模建模。
英文摘要：
Nonlinear photoionization of dielectrics and semiconductors is widely treated in the frames of the Keldysh theory whose validity is limited to small photon energies compared to the band gap and relatively low laser intensities. The time-dependent density functional theory (TDDFT) simulations, which are free of these limitations, enable to gain insight into non-equilibrium dynamics of the electronic structure. Here we apply the TDDFT to investigate photoionization of silicon crystal by ultrashort laser pulses in a wide range of laser wavelengths and intensities and compare the results with predictions of the Keldysh theory. Photoionization rates derived from the simulations considerably exceed the data obtained with the Keldysh theory within the validity range of the latter. Possible reasons of the discrepancy are discussed and we provide fundamental data on the photoionization rates beyond the limits of the Keldysh theory. By investigating the features of the Stark shift as a function of photon energy and laser field strength, a manifestation of the transient Wannier-Stark ladder states have been revealed which become blurred with increasing laser field strength. Finally, it is shown that the TDDFT simulations can potentially provide reliable data on the electron damping time that is of high importance for large-scale modeling.
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