标题： 共振膜超表面中的非常规高次谐波生成 显示英文标题

标题： Unconventional high-harmonic generation in resonant membrane metasurfaces

摘要： 高次谐波生成（HHG）在固体中迅速发展成为一个有前景的平台，用于创建紧凑的阿托秒光源和探测超快电子动力学。 共振超表面对于通过局部场增强来提高原本微小的谐波生成效率至关重要，并且对于避免相位匹配约束的需求也至关重要。 到目前为止，人们认为超表面增强的HHG遵循适用于非共振体HHG的传统整数幂律。 在这里，我们发现由连续态中的准束缚态驱动的高度共振超表面打破了这一原理，表现出所生成谐波功率的非整数强度依赖性。 我们通过实验和理论表明，这些非常规非线性来源于高-Q共振，这些共振产生足够强的局部场，从而显著改变高阶极化率张量对系统有效非线性的贡献。 我们的发现揭示了基于共振场驱动的有效非线性极化率修改的谐波生成如何重塑我们对纳米尺度光-物质相互作用的理解。 显示英文摘要

摘要： High-harmonic generation (HHG) in solids has rapidly emerged as a promising platform for creating compact attosecond sources and probing ultrafast electron dynamics. Resonant metasurfaces are essential for enhancement of the otherwise small harmonic generation efficiency through local field enhancement and are essential to circumvent the need of phase matching constraints. Until now, the metasurface-enhanced HHG was believed to follow the conventional integer-power scaling laws that hold for non-resonant bulk HHG. Here, we discover that highly resonant metasurfaces driven by quasi-bound states in the continuum break this principle, manifesting non-integer intensity dependencies of the generated harmonic powers. We show experimentally and theoretically that these unconventional nonlinearities arise from the high-Q resonances that generate local fields strong enough to substantially alter the contribution of higher order susceptibility tensors to the effective nonlinearities of the system. Our findings reveal how harmonic generation rooted in resonant field-driven modification of effective nonlinear susceptibilities can reshape our understanding of light-matter interaction at the nanoscale.