We study theoretically and experimentally the nonlinear THz emission from plasmonic metasurfaces and show that a thin indium-tin oxide (ITO) film significantly affects the nonlinear dynamics of the system. Specifically, the presence of the ITO film leads to 2 orders of magnitude stronger THz emission compared to a metasurface on glass. It also shows a different power law, signifying different dominant emission mechanisms. In addition, we find that the hot-electron dynamics in the system strongly modify the coupling between the plasmonic metasurface and the free electrons in the ITO at the picosecond time scale. This results in striking dynamic THz emission phenomena that were not observed to date. Specifically, we show that the generated THz pulse can be shortened in time and thus broadened in frequency with twice the bandwidth compared to previous studies and to an uncoupled system. Our findings open the door to design efficient and dynamic metasurface THz emitters.

中文翻译：

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近零电子和热电子在增强非线性超表面动态太赫兹发射中的作用

我们在理论上和实验上研究了等离子体超表面的非线性太赫兹发射，并表明薄的氧化铟锡 (ITO) 薄膜显着影响了系统的非线性动力学。具体来说，与玻璃上的超表面相比，ITO 薄膜的存在导致 THz 发射强 2 个数量级。它还显示了不同的幂律，表示不同的主要发射机制。此外，我们发现系统中的热电子动力学在皮秒时间尺度上强烈地改变了等离子体超表面与 ITO 中自由电子之间的耦合。这导致了迄今为止未观察到的惊人的动态太赫兹发射现象。具体来说，我们表明，与以前的研究和非耦合系统相比，所产生的太赫兹脉冲可以在时间上缩短，从而以两倍的带宽扩大频率。我们的发现为设计高效和动态的超表面太赫兹发射器打开了大门。