Enhanced second harmonic generation from Au nanoparticle arrays by femtosecond laser irradiation

Ultrafast laser irradiation of planar Au nanoparticle arrays is shown to double the particle plasmon quality factor and to enhance second harmonic generation 40-fold. It is found that the irradiation induces a morphological change of nano-cylinders into asymmetric droplet-like shapes with reduced surface roughness without altering their lithographically defined locations. These findings can be used to improve the performance of linear and nonlinear plasmonic devices.