Radiation Forces and Momenta in Dielectric Media

Abstract

There has existed a continuing dialogue concerning the proper identification of radiation forces and momenta in dielectric media. I argue herein that a sensible and consistent picture of these forces and momenta is available. That is, the density of electromagnetic momentum $\overrightarrow{\mathbf{G}}$ is given by $\overrightarrow{\mathbf{G}}=\frac{\overrightarrow{\mathbf{S}}}{c^2}$, where $\overrightarrow{\mathbf{S}}$ is Poynting's vector. The forces which are exerted on material objects in dielectric media are associated with changes in both the electromagnetic and mechanical momenta of the media. In fairly broad circumstances, such forces may be found from the rate of change in a pseudomomentum $\overrightarrow{\mathbf{K}}$ given by $\overrightarrow{\mathbf{K}}=\epsilon \overrightarrow{\mathbf{G}}$, where $\epsilon$ is the dielectric constant of the medium.