Scattering, Absorption, and a Detailed Look at the Field Near an Absorbing Particle

Abstract

A radiating system of charges which is radiating into field-free space is necessarily an exporter of energy, and must therefore have access to energy to keep radiating. However, if it is radiating into a region of space already occupied by a strong field of exactly its own frequency, then it may be either an importer or exporter of energy, depending on the phase relationship of its field to the external field. The effect can be large enough that in the case of a passive system of charges not having access to an energy source, enough energy can be imported from the external field to power the radiation by the system, and even to supply further energy if the system is dissipative as well. If we consider these two importations of energy separately, we see the system as a radiation scatterer in the first, and as a radiation absorber in the second, with the second role being dependent on the first in this way of viewing the matter. The efficiency of the energy extraction process is such in the soft x-ray region that the absorbed energy can considerably exceed the scattered energy.