Circular/linear dichroism and anisotropy based on tunable terahertz metasurfaces.

We propose a chiral metasurface with tunable circular/linear dichroism based on graphene. When a circularly polarized (CP) wave is incident, the metasurface can achieve circular dichroism at two frequencies. Under the incidence of linearly polarized (LP) wave, the metasurface exhibits linear dichroism. At a frequency of 1.89 THz, the designed metasurface has an absorption rate of over 99% for right-handed circularly polarized (RCP) wave, and 11% for left-handed circularly polarized (LCP) wave. The circular dichroism equals 0.88. At 3.0 THz, while the absorptance of the metasurface for LCP and for RCP waves is 97% and 17%, respectively. The circular dichroism is 0.80. At 0.76 THz, and the absorption rate of the metasurface for x-polarized and y-polarized waves is 0.95 and 0.22, respectively. The linear dichroism is 0.73. The near-field imaging is realized by using the differential characteristics of the circular dichroism metasurface. In addition, imaging resolution, linear/Circular dichroism, and single-/dual-frequency terahertz absorption can be effectively adjusted by changing the Fermi level of graphene. This structure has good application prospects in tunable imaging and tunable dichroism. [ABSTRACT FROM AUTHOR]