Angle-dependent SHG enhancement from nanoscale doublehole arrays in a gold film

We present enhanced second harmonic generation (SHG) from arrays of overlapping double holes in a gold film with varying angles of incidence. The double-hole structure permits enhanced SHG when the two holes are just overlapping to produces two sharp apexes. For different center-to-center hole spacings, the maximum occurs for different angles, which is attributed to a shift in the linear transmission wavelength peak of the array and to the requirement to break centrosymmetry for SHG.