Optical properties of dissipative media

General expressions for the optical properties of dissipative media are developed within a framework which retains the separate identities of conduction and polarization currents. The resulting formalism thereby facilitates the physical interpretations that the displacement of bound charges produces polarization while at the same time the motion of free carriers produces conduction currents. The ability of the approach to achieve a clear and consistent physical interpretation of the origins of dispersion in semiconductors is then illustrated by application to the Drude-Lorentz electron model. Finally, the results are related to those based on the conventional treatment wherein effective optical properties are introduced and hence the distinction between conduction and polarization currents does not exist.