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

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 n (eff) near the response frequency despite of the positive nonlinear refractive property of the silica substrate. However, the most strongly negative n (eff) 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.