Fano-type slit modes are essential in high-Q metallic metamaterials, utilizing subwavelength metallic slits to create asymmetric unit cells. In article number 1800041, Gun-Sik Park and his team explore ways to maximize the trapping of electromagnetic Cerenkov radiation waves, enhancing their interaction with electron beams. They also focus on controlling radiation damping, akin to Rayleigh scattering, to improve the efficiency of Cerenkov lasing. – Journal cover design by scapiens