Second Harmonic Generation from a Nanopatterned Isotropic Nonlinear Material

Second harmonic generation (SHG) from a nanopatterned isotropic nonlinear material (GaAs) located inside the subwavelength gaps of a metallic coaxial array is demonstrated. The SHG results from the strong electromagnetic fields in the vicinity of the coaxial gaps; the signal strength is comparable to that from z -cut LiNbO 3 even though the path length is much shorter (∼100 nm compared to 14 μm). Numerical simulations are in good agreement with the experimental data. The observation of a peak-wavelength blue shift between the SH spectrum and the linear transmission spectrum is explained.