Abstract

Plasmon resonances of metal nanoparticles can lead to strong local electromagnetic fields near the particles and thus enhance their optical response. Nanoscale variations in the local fields can also enable magnetic dipoles and electric quadrupoles to contribute to the optical responses [1]. Very small nanoscale features, such as defects, can also support their own plasmonic modes and thereby modify optical responses [2]. We have earlier observed interference between electric dipoles and higher multipoles in second-harmonic generation (SHG) from arrays of metal nanoparticles [3] and interpreted this in terms of the local defect modes [4]. In this paper, we confirm this interpretation and show that the effect of higher multipoles in SHG is almost completely suppressed when new samples with significantly improved quality are used. Furthermore, we show that the overall SHG response from the new samples is about an order of magnitude higher than from the earlier samples.

© 2011 IEEE