Modification of the Absorption Cross Section in the Optical Near-field

The optical interaction of light and matter is modeled as an oscillating dipole in a plane wave. We analyze absorption, scattering and extinction for this system by the energy flow, which is depicted by streamlines of the Poynting vector. Depending on the dissipative damping of the oscillator, the streamlines end up in the dipole. Based on a graphical investigation of the streamlines, this represents the absorption cross section, and forms a far-field absorption aperture. In the near-field of the oscillator, a modification of the aperture is observed. This scheme can be adapted to a single dipolar emitter, interacting with a light field. In the case of the absorption by a single atom, where the oscillator has a circular dipole characteristics, we model the energy flow and derive the apertures.