Reconfigurable Smith-Purcell emission enabled by a chirped metagrating

Smith-Purcell radiation (SPR) is a powerful light-generation mechanism, but the devices are limited by static grating geometries. The authors introduce a reconfigurable SPR modulation on a two-dimensional chirped metallic metagrating without changing the nanostructure. By shifting the electron beam, the system delivers tunable emission angles, switchable focal spots, dual-focus functionality, and dual-wavelength output. Angle-resolved cathodoluminescence experiments reveal precise control of SPR dispersion. This work demonstrates a versatile free-electron photonic platform, paving the way for actively tunable, multifunctional light sources for integrated photonic applications.