Terahertz flat-top beam generation via triple-polarization-channel multiplexed metasurface

• Generation of circular, rectangular, and square flat-top beams in three polarization channels. • GS algorithm is combined with accurate Jones matrix construction to design the metasurface. • The metasurface achieves an overall energy conversion efficiency exceeding 70 %. Different from laser sources, terahertz emitters typically generate beams with spatial inhomogeneity and small aperture size due to limited power. This can limit system performance in applications such as imaging. Optical components for beam shaping are highly desirable. Leveraging metasurfaces' versatile wavefront manipulation capabilities and a non-orthogonal polarization multiplexing strategy, we demonstrate the simultaneous generation of terahertz flat-top beams in three distinct polarization channels. Specifically, circular, rectangular, and square beam profiles are achieved in the x -polarized, 45°, and y -polarized channels, respectively. By implementing the Gerchberg-Saxton angular spectrum iterative algorithm and constructing a full-parameter Jones matrix model, the generated flat-top beams with negligible crosstalk exhibit remarkable improvements in both intensity uniformity and edge steepness compared to the original terahertz source. These advancements enable precise radiation pattern engineering, addressing critical requirements across diverse terahertz applications.