The generation of radiation from free electrons passing a grating, known as Smith-Purcell radiation, finds various applications including non-destructive beam diagnostics and tunable light sources, ranging from terahertz towards X-rays. So far, the gratings used for this purpose have been designed manually, based on human intuition and simple geometric shapes. Here we apply the computer-based technique of nanophotonic inverse design to build a 1400nm Smith-Purcell radiator for sub-relativistic 30 keV electrons. We demonstrate that the resulting silicon nanostructure radiates with a 3-times-higher efficiency and 2.2-times-higher overall power than previously used rectangular gratings. With better fabrication accuracy and for the same electron-structure distance, simulations suggest a superiority by a factor of 96 in peak efficiency. While increasing the efficiency is a key step needed for practical applications of free-electron radiators, inverse design also allows to shape the spectral and spatial emission in ways inaccessible with the human mind.
Observation of the Inherent Chiral Smith-Purcell Effect via Symmetry Breaking
Singapore University of Technology and Design (SUTD)（新加坡科技设计大学）；Nanjing University（南京大学）；Institute of High Performance Computing (IHPC), Agency for Science, Technology, and Research (A*STAR)（新加坡科技研究局高性能计算研究所）；Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology, and Research (A*STAR)（新加坡科技研究局材料研究与工程学院）；National University of Singapore（新加坡国立大学）；Quantum Innovation Centre (Q.InC), Agency for Science, Technology, and Research (A*STAR)（新加坡科技研究局量子创新中心）
Internal Smith-Purcell radiation and its interplay with Cherenkov diffraction radiation in silicon -- a combined time and frequency domain numerical study
University of Electronic Science and Technology of China（电子科技大学）；Terahertz Radiation and Application Key Laboratory of Sichuan Province（四川省太赫兹辐射与应用重点实验室）；National Key Laboratory of Science and Technology on Vacuum Electronics（真空电子学科学与技术国家级重点实验室）；Technion–Israel Institute of Technology（以色列理工学院）；Xian University of Technology（西安理工大学）
Active steering of cathodoluminescence through a generalized Smith-Purcell effect
University of Southern Denmark（南丹麦大学）；NWO Institute AMOLF（荷兰皇家艺术与科学院AMOLF研究所）；Max-Born-Institut（马克斯·玻恩研究所）；ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology（ICFO-光子科学研究所，巴塞罗那科学技术研究所）；ICREA-Institució Catalana de Recerca i Estudis Avançats（加泰罗尼亚高级研究学院）；Danish Institute for Advanced Study, University of Southern Denmark（南丹麦大学丹麦高等研究院）
