Abstract Diamond has attracted great interest as an appealing material for various applications ranging from classical to quantum optics. To date, Raman lasers, single photon sources, quantum sensing and quantum communication have been demonstrated with integrated diamond devices. However, studies of the nonlinear optical properties of diamond have been limited, especially at the nanoscale. Here, a metasurface consisting of plasmonic nanogap cavities is used to enhance both χ (2) and χ (3) nonlinear optical processes in a wedge-shaped diamond slab with a thickness down to 12 nm. Multiple nonlinear processes were enhanced simultaneously due to the relaxation of phase-matching conditions in subwavelength plasmonic structures by matching two excitation wavelengths with the fundamental and second-order modes of the nanogap cavities. Specifically, third-harmonic generation (THG) and second-harmonic generation (SHG) are both enhanced 1.6 × 107-fold, while four-wave mixing is enhanced 3.0 × 105-fold compared to diamond without the metasurface. Even though diamond lacks a bulk χ (2) due to centrosymmetry, the observed SHG arises from the surface χ (2) of the diamond slab and is enhanced by the metasurface elements. The efficient, deeply subwavelength diamond frequency converter demonstrated in this work suggests an approach for conversion of color center emission to telecom wavelengths directly in diamond.

中文翻译：

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使用等离子体纳米间隙谐振器的基于超表面的金刚石变频器

摘要 金刚石作为一种具有吸引力的材料，在从经典光学到量子光学的各种应用中引起了极大的兴趣。迄今为止，拉曼激光器、单光子源、量子传感和量子通信已经用集成金刚石器件进行了演示。然而，对金刚石非线性光学特性的研究一直受到限制，尤其是在纳米级。在这里，由等离子体纳米间隙腔组成的超表面用于增强楔形金刚石板中的 χ (2) 和 χ (3) 非线性光学过程，厚度低至 12 nm。由于通过将两个激发波长与纳米间隙腔的基本和二阶模式相匹配，亚波长等离子体结构中的相位匹配条件的松弛，多个非线性过程同时得到增强。具体来说，三次谐波生成 (THG) 和二次谐波生成 (SHG) 都增强了 1.6 × 107 倍，而与没有超表面的金刚石相比，四波混合增强了 3.0 × 105 倍。尽管金刚石由于中心对称性而缺乏块体 χ (2)，但观察到的 SHG 来自金刚石板的表面 χ (2) 并被超表面元素增强。这项工作中展示的高效、深亚波长金刚石变频器提出了一种将色心发射直接在金刚石中转换为电信波长的方法。观察到的 SHG 来自金刚石板的表面 χ (2)，并被超表面元素增强。这项工作中展示的高效、深亚波长金刚石变频器提出了一种将色心发射直接在金刚石中转换为电信波长的方法。观察到的 SHG 来自金刚石板的表面 χ (2)，并被超表面元素增强。这项工作中展示的高效、深亚波长金刚石变频器提出了一种将色心发射直接在金刚石中转换为电信波长的方法。