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 LiNbO3 even though the path length is much shorter (similar to 100 nm compared to 14 Am). 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.