Title: Dynamic and Continuous Control of Second-Harmonic Chirality through Lithium Niobate Nonlocal Metasurface Show Chinese title

Title: 通过锂铌酸非局域超表面动态和连续控制二次谐波色散

Abstract: Nonlinear chiral light sources are crucial for emerging applications in chiroptics, including ultrafast spin dynamics and quantum state manipulation. However, achieving precise and dynamic control over nonlinear optical chirality with natural materials and metasurfaces, particularly those based on non-centrosymmetric materials such as lithium niobate (LN), is hindered by the complex tensorial nature of the second-order nonlinear susceptibility. Here, we demonstrate a nonlinear nonlocal metasurface, comprising plasmonic nanoantennas atop an x-cut LN thin film, that enables dynamic and continuous control of second-harmonic (SH) chirality. By leveraging two spectrally detuned resonances arising from the excitation of orthogonally propagating guided modes, enabled by lattice anisotropy and LN birefringence, we achieve full-range tuning of SH chirality, from right- to left-handed circular polarization, simply by rotating the polarization of a linearly polarized pump. The SH chirality, quantified by the Stokes parameter S3, is thereby continuously tuned from 0.991 to -0.993 in simulations and from 0.920 to -0.815 in experiments, while maintaining consistently enhanced SH intensity across the entire tuning range. Our approach opens new avenues for developing compact and tunable chiral sources, with potential applications in integrated nonlinear photonics and adaptable quantum technologies. Show Chinese abstract

Abstract: 非线性手性光源在手性光学的新兴应用中至关重要，包括超快自旋动力学和量子态操控。 然而，使用天然材料和超表面实现对非线性光学手性的精确和动态控制，特别是基于非中心对称材料（如铌酸锂（LN））的材料，由于二阶非线性极化率的复杂张量性质而受到阻碍。 在此，我们展示了一种非线性非局部超表面，由位于x切LN薄膜上的等离激元纳米天线组成，该结构能够实现对二次谐波（SH）手性的动态和连续控制。 通过利用由正交传播导模激发产生的两个光谱偏移的共振，这些共振由晶格各向异性和LN双折射性所实现，我们实现了从右旋到左旋圆偏振的SH手性的全范围调制，只需旋转线偏振泵浦的偏振方向即可。 SH手性通过斯托克斯参数S3进行量化，在模拟中从0.991连续调制到-0.993，在实验中从0.920调制到-0.815，同时在整个调制范围内保持增强的SH强度。 我们的方法为开发紧凑且可调的手性光源开辟了新途径，具有在集成非线性光子学和适应性量子技术中的潜在应用。