Spin-Selective Second-Harmonic Vortex Beam Generation with Babinet-Inverted Plasmonic Metasurfaces

Metasurfaces have drawn considerable attentions for their revolutionary capability of tailoring the amplitude, phase, and polarization of light. By integrating the nonlinear optical processes into metasurfaces, new wavelengths are introduced as an extra degree of freedom for further advancing the device performance. However, most of the existing nonlinear plasmonic metasurfaces are based on metallic nanoantennas as meta-atoms, suffering from strong background transmission, low laser damage threshold and small nonlinear conversion efficiency. Here, Babinet-inverted plasmonic metasurfaces made of C-shaped nanoapertures as meta-atoms are designed and demonstrated to solve these issues. Rotation-gradient nonlinear metasurfaces are further constructed for producing spin-selective second-harmonic vortex beams with the orbital angular momentum (OAM) and beam diffraction angle determined by both the spin states of the fundamental wave and second-harmonic emission. The results enable new types of functional metasurface chips for applications in spin, OAM, and wavelength multiplexed optical trapping, all-optical communication, and optical data storage.