Nanoscale variations in the local fields and material properties can enable higher-multipole (magnetic-dipole and electric-quadrupole) contributions to the nonlinear response in addition to electric-dipole contributions. Moreover, the local-field distribution in the structure is important to achieve favorable interaction with the locally varying nonlinearity. Local-field enhancement is particularly important for nonlinear optical effects. Extremely small features of a few nm, such as nanogaps between two particles, are expected to be particularly beneficial for field localization and enhancement. Here, we provide evidence of multipole interference in polarized secondharmonic generation from arrays of L-shaped gold nanoparticles. We also prepare T-shaped gold nanodimers and vary the size of the nanogap between their vertical and horizontal bars. Surprisingly, the second-harmonic signals do not decrease trivially with increasing gap size, because the gap region is nearly centrosymmetric, thereby forbidding second-order effects. Instead, asymmetric local fundamental field distributions along the dimer perimeter are favorable, in accordance with the symmetry rule.

Date Published: 28 September 2007
PDF: 10 pages
Proc. SPIE 6641, Plasmonics: Metallic Nanostructures and Their Optical Properties V, 66410P (28 September 2007); doi: 10.1117/12.731234

Published in SPIE Proceedings Vol. 6641:
Plasmonics: Metallic Nanostructures and Their Optical Properties V
Mark I. Stockman, Editor(s)