Observation of Analog Flatland Cherenkov Radiations on Metasurfaces

Recent theoretical studies have suggested the existence of a lower-dimensional version of the Cherenkov radiation, known as "flatland Cherenkov radiation" (FCR). FCR is generated by leakage from a surface-wave waveguide while being entirely confined in a plane. Here, a metasurface platform is proposed for generating and observing FCR, which is characterized by alternated regions of capacitive and inductive surface impedance, supporting transverse electric (TE) and magnetic (TM) surface waves (SWs), respectively. For experimental demonstration, a microwave setup is presented, and measured results are compared with numerical simulations and theoretical predictions. The study shows that the phase velocities of different SWs can be controlled by structural designs, and suitably fast TE SWs can excite FCR in the form of slower TM SWs. FCR has unique properties such as directionality, tunability, and subwavelength confinement. The proposed platform has important potential to enable nanophotonic applications based on 2D optics, such as agile waveguiding and scanning.Cherenkov radiation is successfully confined within a flatland photonic device, preventing any escape into free space. Employing surface segmentation with varying impedances enables controlled surface waves with different phase velocities. Surface waves with faster phase velocity can excite slower surface waves. This approach allows precise tuning of the propagation angle of surface Cherenkov radiation.image