Radiation Pressure and the Photon Momentum in Dielectrics

We review the magnitudes of the photon momenta in free space, derived by Maxwell and Einstein, and those in homogeneous, dispersionless and lossless dielectrics, associated with Abraham and Minkowski. These momenta determine the forces exerted by light beams on material objects, as measured in radiation pressure experiments. It is shown that conservation conditions for components of the electromagnetic energy–momentum tensors derived by Abraham and Minkowski, also by Einstein and Laub, are equivalent relations simply derived from Maxwell's equations. The challenge for theory is the reliable interpretation of experimental momentum transfers from light to matter, which requires extensions of the basic theory to include material dispersion and surface effects. The main experiments are reviewed, together with details of a Lorentz-force theory that accounts for them. It is shown that the Abraham kinetic momentum is associated with the overall motion of a dielectric sample, while the Minkowski canonical momentum applies to the motion of bodies embedded in the dielectric. 1. Introduction The study of radiation pressure has a long history, dating back at least to a 1619 suggestion by Kepler of its role in the orientation of comet tails in directions pointing away from the sun. The incorporation of the effect into modern theoretical physics was accomplished by Maxwell [1], who showed how the phenomenon of electromagnetic momentum was included in his unified theory. The free-space momentum density in modern notation is given by