Second harmonic generation microscopy is used for the investigation of the nonlinear optical response of single gold nanowires and aggregates of quasi-spherical gold nanomaterials. Angular and spectral resolved approaches are performed to study the origin of the second harmonic emission (SH) from isolated gold nanowire, nanosphere and interacting nanospheres in aggregates. It is observed that the Second harmonic efficiency is enhanced when the excitation wavelength is resonant with the surface plasmon mode (SP) of the metallic nanomaterials. The angular resolved second harmonic analysis study demonstrated the presence of different origins (dipolar, quadrupolar and octupolar modes) involved in the nonlinear optical emission from gold nanowires and nanospheres. Our investigation demonstrates the important role of electric dipole arising from the breaking of the centrosymmetry at the surface of the nanowire and imperfect spherical shape of the gold nanospheres, and in the size regime below 50 nm. The increase of the aggregate and nanowire size induces the presence of interferences between higher orders (quadrupole) and dipole sources. For size higher than 50 nm, the analysis of the angular resolved emission pattern demonstrates the presence of retardation effects and the deviation from the dipolar emission picture. The results are in good agreement with the actual reported results in terms of character of emission. Finally, the SH emission of gold nanowire was spectrally analyzed for single gold nanowire and variable aggregates size. A clear SH emission is observed at 2ω for each excitation frequency ω with the presence of 2 photons visible photoluminescence emission (2PL).

Date Published: 11 September 2013
PDF: 17 pages
Proc. SPIE 8809, Plasmonics: Metallic Nanostructures and Their Optical Properties XI, 880913 (11 September 2013); doi: 10.1117/12.2016939

Published in SPIE Proceedings Vol. 8809:
Plasmonics: Metallic Nanostructures and Their Optical Properties XI
Mark I. Stockman, Editor(s)