Optical second harmonic generation in plasmonic metasurfaces is gaining significant interest to exploit simultaneously the strong near-field enhancement in meta-atoms and the radiation control inherent to metamaterials. Here, we propose a new approach to enhance and control the second harmonic generation beyond the standard nonlinear reflection law. A localized and a propagating plasmon modes are combined in a reflective phase-gradient metasurface composed of silver nanorods on the top of a silver mirror. Due to the phase evolution over the metasurface, the reflected second harmonic beam angle differs from that of the incident beam, contrary to the second harmonic generation from standard interfaces. The second harmonic generation from the metasurface is observed using a nonlinear Fourier microscope and the underlying mechanisms are revealed using full-wave 3D simulations. Interestingly, the second harmonic light is mainly generated by the silver plate and corresponds to anomalous nonlinear reflection following a generalized nonlinear reflection law. These results reveal a new paradigm for the control of nonlinear light conversion at interfaces.
Olivier J. F. Martin, "Metasurface nonlinear optics beyond the standard laws of reflection (Conference Presentation)," Proc. SPIE 10719, Metamaterials, Metadevices, and Metasystems 2018, 107191M (Presented at SPIE Nanoscience + Engineering: August 22, 2018; Published: 17 September 2018); https://doi.org/10.1117/12.2321173.5836038465001.
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