金属表面可控沉积超薄离子层调谐高次谐波产生
Tuning High-Harmonic Generation by Controlled Deposition of Ultrathin Ionic Layers on Metal Surfaces
摘要：
利用半导体和绝缘体产生高次谐波是一个非常活跃的研究领域，因为它具有发展小型高次谐波器件的巨大潜力。在这里，我们表明，通过生长单层（ML）的单晶金属表面上的绝缘体，可以调整谐波光谱，只是改变厚度的绝缘层，而不是激光性能。基于文献中可用的实际电势，$n$ ML NaCl/Cu（111）系统（$n=1-50$）的含时薛定谔方程的数值解表明了这一点。值得注意的是，谐波截止随着$n$线性增加，并且当从$n$ $=$ 1到30时，谐波截止增加多达一个数量级，同时保持激光强度低并且波长在近红外范围内。此外，以这种方式可以实现的控制程度比通过改变激光强度高得多。这种行为的起源是当从与少ML系统相关的基本上离散的能谱移动到扩展周期系统固有的连续能谱（带）时电子“摩擦”的减少。
英文摘要：
High harmonic generation (HHG) from semiconductors and insulators has become a very active area of research due to its great potential for developing compact HHG devices. Here we show that by growing monolayers (ML) of insulators on single-crystal metal surfaces, one can tune the harmonic spectrum by just varying the thickness of the ultrathin layer, not the laser properties. This is shown from numerical solutions of the time-dependent Schrödinger equation for $n$ML NaCl/Cu(111) systems ($n=1-50$) based on realistic potentials available in the literature. Remarkably, the harmonic cutoff increases linearly with $n$ and as much as an order of magnitude when going from $n$ $=$ 1 to 30, while keeping the laser intensity low and the wavelength in the near-infrared range. Furthermore, the degree of control that can be achieved in this way is much higher than by varying the laser intensity. The origin of this behavior is the reduction of electronic "friction" when moving from the essentially discrete energy spectrum associated with a few-ML system to the continuous energy spectrum (bands) inherent to an extended periodic system.
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