Li Yaolong, Jiang Pengzuo, Lyu Xiaying, Li Xiaofang, Qi Huixin, Tang Jinglin, Xue Zhaohang, Yang Hong, Lu Guowei, Sun Quan, Hu Xiaoyong, Gao Yunan, Gong Qihuang
State Key Laboratory for Mesoscopic Physics & Department of Physics, Collaborative Innovation Center of Quantum Matter and Frontiers Science Center for Nano-optoelectronics, Beijing Academy of Quantum Information Sciences, Peking University, 100871, Beijing, China.
Peking University Yangtze Delta Institute of Optoelectronics, 226010, Nantong, Jiangsu, China.
Nat Commun. 2023 Aug 10;14(1):4837. doi: 10.1038/s41467-023-40603-4.
Low-loss dielectric modes are important features and functional bases of fundamental optical components in on-chip optical devices. However, dielectric near-field modes are challenging to reveal with high spatiotemporal resolution and fast direct imaging. Herein, we present a method to address this issue by applying time-resolved photoemission electron microscopy to a low-dimensional wide-bandgap semiconductor, hexagonal boron nitride (hBN). Taking a low-loss dielectric planar waveguide as a fundamental structure, static vector near-field vortices with different topological charges and the spatiotemporal evolution of waveguide modes are directly revealed. With the lowest-order vortex structure, strong nanofocusing in real space is realized, while near-vertical photoemission in momentum space and narrow spread in energy space are simultaneously observed due to the atomically flat surface of hBN and the small photoemission horizon set by the limited photon energies. Our approach provides a strategy for the realization of flat photoemission emitters.
低损耗介电模式是片上光学器件中基本光学元件的重要特征和功能基础。然而，介电近场模式难以通过高时空分辨率和快速直接成像来揭示。在此，我们提出一种方法来解决这个问题，即将时间分辨光发射电子显微镜应用于低维宽带隙半导体六方氮化硼（hBN）。以低损耗介电平面波导作为基本结构，直接揭示了具有不同拓扑电荷的静态矢量近场涡旋以及波导模式的时空演化。利用最低阶涡旋结构，在实空间中实现了强纳米聚焦，同时由于hBN的原子级平整表面以及有限光子能量所设定的小光发射视界，在动量空间中观察到近垂直光发射，在能量空间中观察到窄展宽。我们的方法为实现平面光发射体提供了一种策略。
