Direction-sensitive Smith-Purcell radiation from asymmetric dielectric metagratings.

Here, we report what we believe to be a novel phenomenon of direction-sensitive Smith-Purcell radiation (SPR) mechanism enabled by symmetry-broken all-dielectric metagratings, which facilitates deterministic reconfigurability of radiative wavefronts across the entire spatial domain. By deliberately breaking the spatial symmetry of the mirror-symmetric metagrating pre-engineered to support static unilateral SPR, it allows the radiation directionality to be intrinsically determined by the incidence direction of charged particles (CPs). Consequently, these symmetry-broken metagratings generate upward radiation when CPs are moving forward, and downward radiation when their direction is reversed. This asymmetric radiative behavior originates from the tailored interference of Bloch harmonics within the metagratings. Our findings establish a distinct paradigm for spatially controlling the radiative abilities of SPR, paving the way for direction-resolved particle detectors and multifunctional on-chip light sources.