Generalized description of the nonlinear optical force in laser trapping of dielectric nanoparticles

A general description to estimate optical trapping efficiencies for dielectric nanoparticles using dipole approximation is presented including the effect of optical nonlinearity. We show how optical nonlinearity can be harnessed to trap particles having a refractive index less than that of the surrounding medium. We also discuss optical trapping efficiencies of particles made of metamaterials of negative refractive indices. These results are promising in having wide-ranging applications in photonics science and technology.