Nonlinear optical metasurfaces provide nanoscale‐level control of harmonic waves, making them highly promising platforms for both fundamental research and applications in nonlinear optics. However, the traditional selection rules theory, which has long served as a guiding principle for nonlinear meta‐optics, is local and neglects the significance of meta‐atomic lattice symmetry. In addition, achieving high‐efficiency harmonic generation along with nonlinear optical Pancharatnam‐Berry (PB) phase control remains challenging. To this end, a novel global selection rule jointly determined by the symmetries of both meta‐atom and lattice is proposed. Nonlinear metasurfaces designed based on this theory enable frequency conversions forbidden by previous local selection rules. A more comprehensive relationship between the nonlinear PB phase and the meta‐atomic rotation angle is revealed. Moreover, an efficient nonlinear PB metasurface platform for second harmonic generations is first demonstrated using LiNbO3 thin films with aligned crystal orientations in a hybrid design. The normalized conversion efficiency reaches approximately two orders of magnitude higher than that of existing nonlinear PB metasurfaces working in the near‐infrared band. These findings not only shed light on the underlying mechanisms of nonlinear light‐matter interactions, but also open up exciting possibilities in terahertz, entangled photon pairs, and high harmonic generations.

中文翻译：

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LiNbO3 非线性超光学器件中的全局选择规则和巨型增强谐波产生


非线性光学超表面提供对谐波的纳米级控制，使其成为非线性光学基础研究和应用的非常有前途的平台。然而，长期以来一直是非线性超光学指导原则的传统选择规则理论是局部的，忽视了超原子晶格对称性的重要性。此外，实现高效谐波产生以及非线性光学 Pancharatnam-Berry （PB） 相位控制仍然具有挑战性。为此，提出了一种新的全局选择规则，该规则由超原子和晶格的对称性共同决定。基于该理论设计的非线性超表面实现了以前的局部选择规则所禁止的频率转换。揭示了非线性 PB 相和超原子旋转角度之间的更全面关系。此外，首先在混合设计中使用具有对齐晶体取向的 LiNbO3 薄膜展示了用于二次谐波产生的高效非线性 PB 超表面平台。归一化转换效率比在近红外波段工作的现有非线性 PB 超表面高出大约两个数量级。这些发现不仅阐明了非线性光-物质相互作用的潜在机制，而且为太赫兹、纠缠光子对和高谐波产生开辟了令人兴奋的可能性。