Cubic Nonlinearity of Ag/Au Coreshells

Cubic nonlinearity of Ag/Au spherical coreshells in toluene were investigated by polarization-resolved degenerate four-wave mixing with 6-ns laser pulse at 532 nm with 10-Hz repetition. The average diameter of Ag core was $\sim $6.7 nm. The overall diameter of Ag/Au was changed from 6.1 to 9.1 nm by adding more mole concentration of HAuCl$_{4}$, which resulted in the change of surface plasmon resonance peaks from 411 to 492 nm. The hyperpolarizability of Ag/Au coreshells with parallel and orthogonal excitations were changed from $\sim $3.4$\times $10$^{-38}$ to $\sim $2.7$\times $10$^{-40}$ m$^{5}$/V$^{2}$ and from $\sim $2.5$\times $10$^{-38}$ to $\sim $1.1$\times $10$^{-40}$ m$^{5}$/V$^{2}$, respectively, as the shell thickness of Au was increased. It implies that dephase or decay rates of materials have main contributions on cubic nonlinearity rather than excitation cross-section. This work at Hampton University was supported by Army Research Office (W911NF-07-1-0608) and National Science Foundation (HRD-0734635, HRD-0630372, ESI-0426328/002, and EEC-0532472).