Spectral Dependence Of The Third-Order Optical Susceptibility Of Au Nanostructures: Experiments And First-Principles Calculations

The surface plasmon resonances of Au nanoparticles have attracted wide interest for the promising functionalities in nonlinear plasmonics and nanophotonics in recent decades. However, the third-order susceptibility chi((3)) of Au nanostructures, one of the crucial parameters to describe the nonlinear optical properties, had been experimentally described at only a few wavelengths. These fragmental results have precluded the understanding of the physical origins. Here, we have evaluated the real and imaginary components of chi((3)) in a broad range (1.50-3.10 eV) through a combined analysis of spectroscopic ellipsometry and pump-probe spectroscopy. The results show that the macroscopic and intrinsic chi((3)) are strongly wavelength dependent and consist of several successive peaks. Furthermore, by analyzing and comparing the Au thin film to nanoparticles, the contributions of the interband and intraband transitions in the Au nanoparticle are clarified.