Field quantization in a plasma: photon mass and charge

It is shown here that a straightforward procedure can be used to quantize the linearized equations for an electromagnetic field in a plasma. This leads to a definition of an effective mass for the transverse photons, and a different one for the longitudinal photons, or plasmons. Both masses are simply proportional to the electron plasma density. A nonlinear perturbative analysis can also be used to extend the quantization procedure, in order to include the ponderomotive force effects. This leads to the definition of a photon charge operator. The mean value of this operator, for a quantum state with a photon occupation number equal to 1, is the equivalent charge of the photon in a plasma.