杂化连续域内束缚态中的环形偶极子

Toroidal Dipole in Hybrid Bound States in the Continuum

基于连续域内束缚态(BIC)的超表面具备在时间和空间上实现高效光场调控的能力.在时间维度上,BIC理论上可实现无穷长的辐射光子寿命,因此在激光谐振腔、非线性光学、传感等领域展现了极好的应用价值.为深入理解BIC及衍生谐振特性,基于双开口金属谐振器构成的杂化BIC超表面,探讨由于能带折叠引起的折叠谐振与准BIC谐振之间的特性.利用数值模拟、多极子分析和太赫兹光谱实验验证环形偶极子在这两类谐振辐射特性中的重要作用.此外,通过对比两种不同能带折叠方式的超晶格,进一步确认环形偶极子对折叠谐振品质因数的调制特性.深入理解谐振中多极子的散射特性对获取高品质因数谐振腔具有重要作用,为切实推动超表面在太赫兹传感、调制器和非线性相互作用等领域的应用奠定理论基础.

Metasurfaces based on bound states in the continuum(BIC)are capable of manipulating light in both temporal and spatial dimensions.In the temporal dimension,BIC possesses an infinite photon lifetime and is widely used in the laser cavity,nonlinear optics,and sensing.In this study,we investigate the properties of band-folded resonances and quasi-BIC based on a hybrid BIC metasurface.The key role of a toroidal dipole in distinguishing the two-type resonances is investigated via multipolar analysis,and numerical simulations,and verified by terahertz experiments.Moreover,hybrid BIC metasurfaces with supercells of different band folding features are compared,further demonstrating the essential role of the toroidal dipole in determining quality factors of these resonances.A deep understanding of the scattering properties of multipolar in resonance plays an important role in obtaining high-quality factor resonant cavities,laying a theoretical foundation for promoting the application of metasurfaces in terahertz sensing,modulators,and nonlinear interactions.