Nonlinear metasurfaces for amplitude-controllable and pump-handedness-selective THz generation

Integrating generation and manipulation processes of terahertz (THz) waves into a single device is crucial for miniaturizing THz systems. Nonlinear metasurfaces have recently emerged as a flexible platform to accomplish this task. However, such existing THz devices have limitations in achieving more controlling freedoms while being multi-functional. In this study, we introduce the coupling effect between different meta-atoms into the unit-cell design and experimentally validate its powerfulness in controlling nonlinear THz generation. Two types of meta-molecules are experimentally demonstrated, where the metamolecule with achiral coupling allows full control over the THz amplitude, while the meta- molecule with chiral coupling makes the THz generation sensitive to the pump handedness. Moreover, the meta-molecule with giant chiral coupling further enables a multiplexing-based handedness-selective nonlinear metasurface, which generates THz beams with different orbital angular momentums (OAMs). This approach holds great promise for developing various integrated nonlinear THz devices.