Terahertz Chiral Metasurface for Dual-Band Spin-Selective Absorption With Strong Circular Dichroism

The spin-selective absorption (SSA) usually means absorbing one spin state of a circular polarized (CP) wave while reflecting the orthogonal one. Here, we propose two types (type 1 and type 2) of dual-band SSA with strong circular dichroism based on chiral metasurface operating at the terahertz region. For the proposed dual-band SSA metasurface, type 1 can absorb the same spin state of a CP wave in two adjacent bands, while type 2 can absorb one spin state of a CP wave in the first band and absorb the orthogonal one in the second band. The physical mechanism of the proposed SSA metasurface is discussed by introducing the multiple interference model with a detailed equation derivation process. The theoretically calculated results are well-consistent with the simulated one. Four samples (including two types of dual-band SSA metasurface and their mirrored structure) were fabricated and measured to demonstrate our strategy. Finally, the THz near-field imaging is implemented based on the proposed dual-band SSA metasurface to demonstrate their potential applications in multiband THz CP wave detection and image encryption.