Movie-mode visualization of terahertz fields inside subwavelength metallic structures using ultrashort relativistic electrons

Strong terahertz (THz) fields enhanced by subwavelength structures have great potential in manipulating the 6D phase space distribution of free electrons. Accurate measurement spatiotemporal THz field inside structure is essential for understanding physics behind such manipulation. Here, we demonstrate a method to directly probe metallic movie mode with ultrashort relativistic Information about encoded into deflected electron beam at various time delays. Using rectangular slits as representative examples, show that can be accurately retrieved. Furthermore, deflection demonstrates factor 20 slit synthesis pulse train. We anticipate this noninvasive way probing electromagnetic electrons find wide applications many areas research.