On-demand multiplexed vortex beams for terahertz polarization detection based on metasurfaces.

The manipulation of polarization states is crucial for tailoring light-matter interactions and has great applications in fundamental science. Nevertheless, conventional polarization measurement approaches are extremely challenging to determine the polarization state of incident terahertz (THz) beams. The combination of metasurfaces and inhomogeneous vector vortex beams (VVBs) provides a new solution for integrated polarization-related functional devices. Herein, a general design strategy for spin-multiplexing all-silicon metasurfaces is presented and demonstrated in THz polarization detection. The employment of basic building blocks with a high aspect ratio (AR) imparts a greater degree of freedom for generating vector beams, and those basic blocks are subsequently utilized to explore the visualized polarization state. With the assistance of a THz near-field scanning system, we evaluate the capability of reconstructing the incident polarization state from the longitudinal polarization component multiplexed by vortex beams with tight focusing characteristics. Not only that, we also utilize the polarization with dynamically varying behavior as the illumination method to elucidate the evolution trend of the polarization state under a single snapshot and establish a visualized parametric model. This work paves the way to realize ultra-compact THz polarization detection-related devices for future applications in remote sensing, high-resolution imaging, and communications.