We establish the time-averaged total force on a subwavelength-sized particle in a time-harmonic-varying field. Our analysis is not restricted to the spatial dependence of the incident field. We discuss the addition of the radiative reaction term to the polarizability to deal correctly with the scattering force. As an illustration, we assess the degree of accuracy of several previously established polarizability models.
We derive the analytic expressions of the electromagnetic force and torque on a dipolar particle, with arbitrary dielectric permittivity and magnetic permeability. We then develop a general framework, based on the coupled dipole method, for computing the electromagnetic force and torque experienced by an object with arbitrary shape, dielectric permittivity and magnetic permeability.
We propose a novel way to trap and manipulate nano-objects above a dielectric substrate using an apertureless near-field probe. A combination of evanescent illumination and light scattering at the probe apex is used to shape the optical field into a localized, three-dimensional optical trap. We use the coupled-dipole method and the Maxwell stress tensor to provide a self-consistent description of the optical force, including retardation and the influence of the substrate. We show that small objects can be selectively captured and manipulated under realistic conditions.
In the coupled dipole method, a three-dimensional scattering object is discretized over a lattice into a set of polarizable units that are coupled self-consistently. Starting from the volume integral equation for the field, we show that performing the integration of the free-space field susceptibility tensor over the lattice cell dramatically improves the accuracy of the method when the permittivity of the object is large. This integration, done without any approximation, allows us to define a prescription for the polarizability used in the coupled dipole method. Our derivation is not restricted to any particular shape of the scatterer or to a cubic discretization lattice.
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