Wang Qingwei, Zhang Xueqian, Xu Quan, Feng Xi, Niu Li, Chen Xieyu, Lu Yongchang, Feng Jian, Fang Ming, Zhang Xixiang, Zhang Weili, Han Jiaguang
Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering, and the Key Laboratory of Optoelectronics Information and Technology, Tianjin University, Tianjin, 300072, P. R. China.
Key Laboratory of Intelligent Computing and Signal Processing, Ministry of Education, Anhui University, Hefei, 230039, P. R. China.
Adv Mater. 2025 Jul;37(30):e2500392. doi: 10.1002/adma.202500392. Epub 2025 May 12.
Terahertz (THz) generation is a crucial initial step in THz applications. However, the current THz sources face challenges in fully controlling the propagation properties of generated THz waves without the use of external devices. This limitation leads to bulky systems with unavoidable insertion losses and bandwidth constraints. To overcome these challenges and facilitate compact and versatile THz applications, a novel approach using nonlinear metasurfaces is proposed to control the amplitude, phase, and polarization of broadband THz waves directly and simultaneously at the emission stage. The basic design features an elaborated coupling-controlled chiral meta-atom, providing adjustable chirality and allowing an independent amplitude and phase control strategy under a circularly polarized (CP) pump. Furthermore, the polarization state of emitted THz wave can be arbitrarily customized by designing the superposition of the generated left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components. This control is linearly predictable, eliminating the need for complex nonlinear simulations and interleaved supercell arrangements. The effectiveness of this method is demonstrated by experimentally generating two types of unique vectorial THz fields: spatial-polarization separable and nonseparable states. The proposed approach significantly enhances the capabilities of nonlinear metasurfaces, paving the way for versatile THz generation devices.
太赫兹（THz）产生是太赫兹应用中的关键初始步骤。然而，当前的太赫兹源在不使用外部设备的情况下，要完全控制所产生太赫兹波的传播特性面临挑战。这种限制导致系统体积庞大，存在不可避免的插入损耗和带宽限制。为了克服这些挑战并促进紧凑且通用的太赫兹应用，提出了一种使用非线性超表面的新方法，以在发射阶段直接且同时地控制宽带太赫兹波的幅度、相位和偏振。基本设计采用了精心设计的耦合控制手性元原子，可提供可调手性，并在圆偏振（CP）泵浦下允许采用独立的幅度和相位控制策略。此外，通过设计所产生的左旋圆偏振（LCP）和右旋圆偏振（RCP）分量的叠加，可以任意定制发射太赫兹波的偏振态。这种控制是线性可预测的，无需复杂的非线性模拟和交错的超胞排列。通过实验产生两种独特的矢量太赫兹场：空间偏振可分离和不可分离状态，证明了该方法的有效性。所提出的方法显著增强了非线性超表面的能力，为通用太赫兹产生装置铺平了道路。
