Determining the optimum thickness for high harmonic generation from nanoscale thin films: An ab initio computational study
Determining the optimum thickness for high harmonic generation from nanoscale thin films: An ab initio computational study
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DOI：
10.1103/physrevb.103.155426
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发表时间：
2021-02
影响因子：
3.7
通讯作者：
S. Yamada;K. Yabana
中科院分区：
文献类型：
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作者：
S. Yamada;K. Yabana
我们从理论上研究高次谐波产生（HHG）从硅薄膜的厚度从几个原子层到几百纳米，以确定最有效的厚度产生强烈的HHG的反射和透射脉冲。为此，我们采用了一些理论和计算方法。最复杂的方法是从头算含时密度泛函理论与麦克斯韦方程在一个共同的空间分辨率。这使我们能够探索这样的影响，如表面电子结构和光的传播，以及电子运动的能带在一个统一的方式。我们还利用多尺度方法，适用于较厚的薄膜。二维近似的介绍，以获得一个直观的理解的厚度依赖性的HHG。从这些从头计算，我们发现，高次谐波信号是最强的薄膜厚度为2-15 nm，这是由硅的体电导率。我们还发现，在反射和透射脉冲的高次谐波信号是相同的，在这样的薄膜。在厚度与介质波长相当的薄膜中，发现反射（透射）脉冲中的高次谐波信号强度与薄膜前（后）表面的电场强度相关。
We theoretically investigate high harmonic generation (HHG) from silicon thin films with thicknesses from a few atomic layers to a few hundreds of nanometers, to determine the most efficient thickness for producing intense HHG in the reflected and transmitted pulses. For this purpose, we employ a few theoretical and computational methods. The most sophisticated method is the ab initio time-dependent density functional theory coupled with the Maxwell equations in a common spatial resolution. This enables us to explore such effects as the surface electronic structure and light propagation, as well as electronic motion in the energy band in a unified manner. We also utilize a multiscale method that is applicable to thicker films. Two-dimensional approximation is introduced to obtain an intuitive understanding of the thickness dependence of HHG. From these ab initio calculations, we find that the HHG signals are the strongest in films with thicknesses of 2-15 nm, which is determined by the bulk conductivity of silicon. We also find that the HHG signals in the reflected and transmitted pulses are identical in such thin films. In films whose thicknesses are comparable to the wavelength in the medium, the intensity of HHG signals in the reflected (transmitted) pulse is found to correlate with the magnitude of the electric field at the front (back) surface of the thin film.