Localized Surface Plasmon Resonance Enhanced Third-Order Nonlinearity of Al Nanoshells in Silica

Abstract

Third-order nonlinear optical properties of Al nanoshells in silica were studied by using the Maxwell-Garnett theory. Simulation results reveal that the third-order nonlinearity of composite can be remarkably enhanced near the localized surface plasmon resonance (LSPR) of Al nanoshells. This enhanced third-order nonlinearity can be achieved in the deep-ultraviolet to near-visible light region by tailoring Al shell thickness. Owing to a phase-shift enhancement of the complex nonlinear refraction induced by Al nanoshells, the composite exhibits a strongly negative nonlinear refraction index neff near the response frequency despite of the positive nonlinear refractive property of the silica substrate. However, the most strongly negative neff occurs on the long wavelength side of LSPR, and this deviation becomes larger with decreasing the shell thickness. This has been interpreted by the size-dependent electron surface scattering. Similarly, the nonlinear susceptibility as well as the corresponding figure of merit also exhibits a strong dependence on the shell thickness.