We provide a self-consistent mean field approximation in the framework of Mie scattering theory to study the optical bistability of a metallic nanoparticle coated with a nonlinear shell. We demonstrate that the nanoparticle coated with a weakly nonlinear shell exhibits optical bistability in a broad range of incident optical intensity. This optical bistability critically relies on the geometry of the shell-coated nanoparticle, especially the fractional volume of the metallic core. The incident wavelength can also affect the optical bistability. Through an optimization-like process, we find a design with broader bistable region and lower threshold field by adjusting the size of the nonlinear shell, the fractional volume of the metallic core, and the incident wavelength. These results may find potential applications in optical bistable devices such as all-optical switches, optical transistors and optical memories.

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We investigate the optical force on the nonlinear nanoparticles with gain based on nonlinear Mie theory and Maxwell’s stress tensor method. For the nonlinear susceptibility χ(3) = 0 (i.e., the linear nanoparticle), the threshold gain to obtain the optical pulling force increases when the permittivity of the surrounding medium εm deviates from the real part of the permittivity of the nanoparticles εcr. For χ(3) > 0, one or two threshold fields exist for the switch of optical pulling and pushing force. However, for χ(3) < 0, only one threshold field is found. Moreover, the optical pulling force may be enhanced by tuning the incident field intensity. Our results for the optical force on the nonlinear nanoparticle will have potential applications in nonlinear optical manipulations and optical transportation.

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