Plasmonic nanowire metamaterials, arrays of aligned plasmonic nanowires grown inside an insulating substrate, have recently emerged as a flexible platform for engineering refraction, diffraction, and density of photonic states, as well as for applications in bio- and acoustic sensing. Majority of unique optical phenomena associated with nanowire metamaterials have been linked to the collective excitation of cylindrical surface plasmons propagating on individual nanowires. From the effective medium standpoint, this collective excitation can be described as an additional electromagnetic wave, emanating from nonlocal effective permittivity of metamaterial. The electromagnetic fields associated with such mode can are strongly inhomogeneous on the scale of the unit cell. In this work we analyze the effect of the strong field variation inside nanowire metamaterial on second harmonic generation (SHG). We show that second harmonic generation is strongly enhanced in the frequency region where metamaterial is nonlocal. Overall, the composite is predicted to outperform its homogeneous metal counterparts by several orders of magnitude. Quantitative description of SHG in nanowire medium is developed. The results suggest that bulk second harmonic polarizability emerges as result of collective surface-enhanced SHG by individual components of the composite.

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Viktor A. Podolskiy, Brian Wells, Giuseppe Marino, and Anatoly V. Zayats, "Nonlinear optics in nonlocal nanowire metamaterials (Conference Presentation)," Proc. SPIE 9918, Metamaterials, Metadevices, and Metasystems 2016, 99180G (Presented at SPIE Nanoscience + Engineering: August 28, 2016; Published: 9 November 2016); https://doi.org/10.1117/12.2239104.5159519588001.