Generalization of Planck's Law of Radiation to Anisotropic Dispersive Media

Abstract

The distribution of radiant energy in media which are not only dispersive but also anisotropic is derived. The distribution is found to depend on the phase velocity 1'., the group velocity V ?? and the angle oc. between them for each mode s. Planck's law is a limiting case when V. = Vas = c and oc. = 0 and applies strictly only to a vacuum.