Compositional-asymmetry influenced non-linear optical processes of plasmonic nanoparticle dimers

Abstract : The influences of compositional asymmetry on the two-photon photoluminescence and the second harmonic generation processes in weakly coupled plasmonic dimers were addressed. Au–Au homodimer and Au–Ag heterodimer arrays produced using electron-beam lithography were investigated using confocal nonlinear optical imaging and spectroscopy. Compared to the Au–Au homodimers, the Au–Ag dimers showed slightly broadened two-photon photoluminescence near the X symmetry point at the first Brillouin zone of Au, whilst that from the L symmetry point stayed the same. Additionally, weakly coupled Au–Ag heterodimers generated strong second harmonic signals which were invisible in the Au–Au homodimers. The observations highlighted the importance of compositional asymmetry in the non-linear optical studies of plasmonic dimers.