Anisotropic nonlinearities in crystalline gold and how to exploit them

We demonstrate a monocrystalline plasmonic metasurface which takes advantage of the anisotropic second-harmonic generation from 111-type gold surface. Furthermore, we provide a comprehensive description of this anisotropic nonlinearity that is rooted in the microscopic symmetries of the crystal, and validate experi- mental results with numerical simulations, which show excellent agreement.