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We propose an alternative way to enhance optical nonlinearity from nanocomposites containing nonlinear bimetallic nanostructures. The optical nonlinearity enhancement are due to two aspects: firstly, the intrinsic large nonlinearity of metallic material in core and shell; secondly, the coupling of dipole modes gives rise to symmetric and antisymmetric resonance, which strengthen the local fields in the core and shell. By fine adjustment of the core-shell size ratio, it is possible to achieve maximal enhancement of optical nonlinearity from bimetallic coated nanocomposites.

We demonstrate the features of the dipole and quadrupole resonant modes in extinction spectra of spherically anisotropic nanoparticles based on full-wave scattering theory. It is found that in a core–shell nanosphere, the introduction of spherical anisotropy in the core leads to a blue shift in resonant wavelengths for small nanoparticles, while, for large nanoparticles (core radius larger than 90 nm), the dipole resonant wavelength remains unchanged with the variation of spherical anisotropy. In addition, the peak strengths for the dipole and quadrupole modes are also studied. Numerical simulations show that the strong localization of electric fields can be further enhanced and tuned by adjusting the spherical anisotropy in the core. In contrast, the anisotropy introduced in the shell results in a blue shift for small nanoparticles but a red shift for nanoparticles with larger size. The tunability of plasmon resonant shifts in extinction spectra and tailored localization of enhanced fields are revealed.

In this paper, we establish the full-wave electromagnetic scattering theory to study the electromagnetic scattering from infinitely long cylinders with cylindrically anisotropic coatings. We show that the total effective scattering width can be dramatically reduced by the suitable adjustment of the dielectric anisotropy of the shell, while it is not the case for tuning the dielectric anisotropy of the core. Furthermore, we could make the cylindrical objects invisible when both dielectric and magnetic anisotropies are adjusted. In the long wavelength limit, we develop effective medium theory to derive the effective isotropic permittivity and permeability for the anisotropic coated cylinders, and the invisibility radius ratio derived from the full-wave theory for small coated cylinders can be well described within the effective medium theory.

Basing on the Electromagnetic scattering theory by coated spheres of radial dielectric anisotropy, we demonstrate the features of the surface plasmon resonance (SPR) of the anisotropic core-shell nanoparticle. It is found that for radially anisotropic core with gold nanoshell, there exists a blue-shift of the SPR wavelengths in contrast to the particle with an isotropic core. For the gold core with radially anisotropic shell, the wavelengths of SPR have a blue-shift for relatively small size nanoparticles, while the wavelengths of SPR have a red-shift for a larger nanoparticle .