Optical pulling force on nonlinear nanoparticles with gain

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.