Dynamic control of reflective chiral terahertz metasurface with a new application developing in full grayscale near field imaging

The chiral metasurface possesses wide applications in terahertz (THz) band. It is still an important issue to control the chiral properties of metasuface by a simple and effective method. We design a reflective chiral THz metasurface that reflection medium in bottom is based on monolayer graphene on low resistance Si substrate. This structure allows a more reasonable approach to tune Fermi level (EF) of graphene compared with previous report. THz reflection change in graphene as varying EF can control in a large dynamic range the chiral properties of metasurface, inducing the state switch between ‘On’ and ‘Off’. The dynamic control is also effective for various further applications such as vortex focusing and near field imaging. Significantly, we report for the first time the variation rule of reflection amplitude for reflecting suppressed circularly polarized light, with the change in rotation angle of top metal ring of metasurface. Based on this, we develop an innovation application, called full grayscale near field imaging (FGNFI) that can show full grayscale details compared with traditional near field imaging that can only show two grayscale states.