Radiation force induced by resonant light: from atom to nanoparticle

We derive analytical expressions for the radiation force induced by electronically resonant light which apply over the size range from atoms to nanoparticles. These are based on the method of Maxwell stress tensor and microscopic response theory. The radiation force is expressed as a sum of a scattering force, an absorbing force and additional terms arising from the asymmetric spatial distribution of the internal field from light-exciton coupled modes. In the case of a particle with a radius of few tens of nm, a particular interesting point is that, under certain conditions, substantially large contributions from these terms appear as forces in opposite direction to the direction of propagation of plane wave light.