Deinert Jan-Christoph, Alcaraz Iranzo David, Pérez Raúl, Jia Xiaoyu, Hafez Hassan A, Ilyakov Igor, Awari Nilesh, Chen Min, Bawatna Mohammed, Ponomaryov Alexey N, Germanskiy Semyon, Bonn Mischa, Koppens Frank H L, Turchinovich Dmitry, Gensch Michael, Kovalev Sergey, Tielrooij Klaas-Jan
Helmholtz-Zentrum Dresden-Rossendorf, Dresden 01328, Germany.
ICFO - Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels (Barcelona) 08860, Spain.
ACS Nano. 2021 Jan 26;15(1):1145-1154. doi: 10.1021/acsnano.0c08106. Epub 2020 Dec 11.
Nonlinear optics is an increasingly important field for scientific and technological applications, owing to its relevance and potential for optical and optoelectronic technologies. Currently, there is an active search for suitable nonlinear material systems with efficient conversion and a small material footprint. Ideally, the material system should allow for chip integration and room-temperature operation. Two-dimensional materials are highly interesting in this regard. Particularly promising is graphene, which has demonstrated an exceptionally large nonlinearity in the terahertz regime. Yet, the light-matter interaction length in two-dimensional materials is inherently minimal, thus limiting the overall nonlinear optical conversion efficiency. Here, we overcome this challenge using a metamaterial platform that combines graphene with a photonic grating structure providing field enhancement. We measure terahertz third-harmonic generation in this metamaterial and obtain an effective third-order nonlinear susceptibility with a magnitude as large as 3 × 10 m/V, or 21 esu, for a fundamental frequency of 0.7 THz. This nonlinearity is 50 times larger than what we obtain for graphene without grating. Such an enhancement corresponds to a third-harmonic signal with an intensity that is 3 orders of magnitude larger due to the grating. Moreover, we demonstrate a field conversion efficiency for the third harmonic of up to ∼1% using a moderate field strength of ∼30 kV/cm. Finally, we show that harmonics beyond the third are enhanced even more strongly, allowing us to observe signatures of up to the ninth harmonic. Grating-graphene metamaterials thus constitute an outstanding platform for commercially viable, CMOS-compatible, room-temperature, chip-integrated, THz nonlinear conversion applications.
非线性光学对于科学和技术应用而言是一个日益重要的领域，这归因于其与光学及光电子技术的相关性和潜力。当前，人们正在积极寻找具有高效转换和小材料占用面积的合适非线性材料体系。理想情况下，该材料体系应允许芯片集成和室温操作。二维材料在这方面极具吸引力。特别有前景的是石墨烯，它在太赫兹波段展现出了异常大的非线性。然而，二维材料中的光与物质相互作用长度本质上是极小的，从而限制了整体的非线性光学转换效率。在此，我们利用一种超材料平台克服了这一挑战，该平台将石墨烯与提供场增强的光子光栅结构相结合。我们测量了这种超材料中的太赫兹三次谐波产生，并在0.7太赫兹的基频下获得了有效三阶非线性极化率，其大小高达3×10 m/V，即21 esu。这种非线性比没有光栅的石墨烯大50倍。这样的增强对应于由于光栅导致强度增大3个数量级的三次谐波信号。此外，我们使用约30 kV/cm的中等场强展示了高达约1%的三次谐波场转换效率。最后，我们表明高于三次的谐波增强更为显著，使我们能够观测到高达九次谐波的信号。因此，光栅 - 石墨烯超材料构成了一个用于商业可行、与CMOS兼容、室温、芯片集成的太赫兹非线性转换应用的杰出平台。
