Smith-Purcell Radiation in Two Dimensions

Smith-Purcell radiation (SPR) is an electromagnetic radiation generated by the motion of free electrons in close to a periodic structure. Over the past 70 years, there has been significant interest in the generation of light in three-dimensional (3D) free space through SPR. Here, by using the interaction between moving electrons and a designed metallic nanoaperture array, the observation of two-dimensional (2D) SPR, e.g., the plasmon polaritons propagating on metal surfaces, is presented. This phenomenon was confirmed using cathodoluminescence under grazing incidence, by decoupling 2D SPR with specially designed optical grating into far field. Moreover, by utilizing the phased array radar effect in 2D, the radiation direction of 2D SPR is demonstrated to be manipulated by rotating the aperture orientation. This work not only expands our understanding of SPR from the 3D to 2D, but also provides a practical approach for controlling the propagation of 2D SPR.