Polarization Shaping of Free-Electron Radiation by Gradient Bianisotropic Metasurfaces

Free-electron radiation phenomena facilitate enticing potential to create light emission with highly tunable spectra, covering hard-to-reach frequencies ranging from microwave to X-ray. Consequently, they take part in many applications such as on-chip light sources, particle accelerators, and medical imaging. While their spectral tunability is extremely high, their polarizability is usually much harder to control. Such limitations are especially apparent in all free electron based spontaneous radiation sources, such as the Smith-Purcell (SP) radiation. Here, anomalous free-electron radiation phenomenon is demonstrated at the microwave regime from gradient bianisotropic metasurfaces, by using a phased dipole array to mimics moving charged particles. The phase gradient and the bianisotropy in metasurfaces provide new degrees of freedom for the polarization shaping of free-electron radiation, going beyond the common spectral and angular shaping. Remarkably, the observed anomalous free-electron radiation obeys a generalized SP formula derived from Fermat's principle.

Automated summary

Free-electron radiation phenomena have great potential in creating light emission with highly tunable spectra, covering a wide range of frequencies from microwave to X-ray. These phenomena can be applied in various fields such as on-chip light sources, particle accelerators, and medical imaging. Anomalous free-electron radiation has been demonstrated at the microwave regime from gradient bianisotropic metasurfaces, utilizing new degrees of freedom in polarization shaping beyond the common spectral and angular shaping.