Abstract
In this work, we investigated, both theoretically and experimentally, the saturable scattering in a single gold nanoparticle for the first time. In theoretical part, we used different models of the nonlinear properties to explain the nonlinear responses in gold material. In experimental part, multi-color confocal microscopy was used to observe the scattering of a single gold nanoparticle. As a result, by a resonant excitation, saturable scattering was observed with moderate excitation intensity (~10<sup>7</sup> W/cm<sup>2</sup>); with even higher excitation intensity (>10<sup>9</sup> W/cm<sup>2</sup>), reverse saturable scattering was observed, indicating the existence of higher order nonlinear properties. To completely comprehend the mechanism of this saturable scattering, we applied three kinds of excitation wavelengths (405nm, 532nm and 671nm) and four kinds of gold nanoparticle with different diameters (40nm, 50nm, 80nm and 100nm) to demonstrate the wavelength dependence and size dependence. Since the scattering of gold nanoparticles is significantly enhanced by localized surface plasmon resonance, we compared these dependencies with the spectral properties induced by LSPR and found that they match the spectra, revealing that the saturation is dominated by plasmon resonance. Besides, by fitting the dependencies, linear and nonlinear hyperpolarizability of a single gold nanoparticle were also deduced.
Published Version
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