Polarization Dependence of Emissivity

where i, r, and t label the incident, reflected, and transmitted waves, respectively. The solution is based on the fact that eq. (1) holds separately for each polarization of the emitted radiation, and is also independent of the angle of the radiation. This result is implicit in Planck’s derivation [5] of Kirchhoff’s law of radiation, and is stated explicitly in [6]. That law describes the thermodynamic equilibrium of radiation emitted and absorbed throughout a volume. The emissivity Pv and the absorption coefficient Aν can depend on the polarization of the radiation and on the angle of the radiation, but the definitions of polarization parallel and perpendicular to a plane of emission, and of angle relative to the normal to a surface element, are local, while the energy conservation relation Pν = AνK(ν, T ) is global. A “ray” of radiation whose polarization can be described as parallel to the plane of emission is, in general, a mixture of parallel and perpendicular polarization from the point of view of the absorption process. Similarly, the angles of emission and absorption of a ray