Terahertz focusing enhancement for graphene-based tunable metalens

We propose a type of hybrid structure metalens composed of a graphene-loaded metallic metasurface sandwiched by two mutually orthogonal gratings, which can work in transmission modes for dynamic terahertz wavefront manipulation with tunability and enhanced focusing efficiency. Experimental results show that due to the multi-reflection between the metasurface layer and the grating layers, the focusing efficiency is enhanced by 1.8 times, and the focal length of the metalens is increased by 0.61mm by increasing the applied gate voltage on the graphene from 0V to 1.4V. We hope the proposed structure may open a new avenue for reconfigurable THz metasurfaces with high efficiencies.