Nonlinear processes are at the core of many optical technologies whose further development require optimized materials suitable for nanoscale integration. Here we demonstrate the emergence of a strong bulk second-order nonlinear response in a plasmonic nanorod composite comprised of centrosymmetric materials. We develop an effective-medium description of the underlying physics, compare its predictions to the experimental results, and analyze the limits of its applicability. We demonstrate strong tunable generation of the $p$-polarized second-harmonic light in response to either $s$- or $p$-polarized excitation. High second-harmonic enhancement is observed for fundamental frequencies in the epsilon-near-zero spectral range. The work demonstrates emergence of structurally tunable nonlinear optical response in plasmonic composites and presents a new nonlinear optical platform suitable for integrated nonlinear photonics.

中文翻译：

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等离子体超材料的结构二阶非线性

非线性工艺是许多光学技术的核心，其进一步发展需要适合纳米级集成的优化材料。在这里，我们证明了在由中心对称材料组成的等离子纳米棒复合材料中，强大的本体二阶非线性响应的出现。我们开发了对基础物理学的有效描述，将其预测结果与实验结果进行了比较，并分析了其适用性的局限性。我们展示了强大的可调一代$p$偏振的二次谐波光响应 $s$- 或者 $p$极化激励。在ε接近零的频谱范围内观察到基本频率具有很高的二次谐波增强。这项工作证明了等离子复合材料中结构可调非线性光学响应的​​出现，并提出了一种适用于集成非线性光子学的新型非线性光学平台。