Emission in nonstationary media

A weak point of the theory of electrodynamics involving nonstationary media is that the wave equations for the scalar and vector potentials and also for the electric and magnetic field intensity vectors possess different operators and, consequently, different phase velocities of the field quantities of the same electromagnetic wave. This difference becomes inessential only in the case of small disturbances. This theoretical inconsistency is removed in the present paper. A rigorous description is obtained for the appearance of a birefringence analog for nonstationary isotropic absorbing media. It is shown that two waves - a TE and a TM wave - are generated and propagate at different phase velocities. One or the other of the rigorous solutions may be used, depending on the disturbance polarization. This eliminates the ambiguity in the determination of the phase velocities.