Electromagnetic Fluctuations in a Cavity

Abstract

The problem of electromagnetic fluctuations in a cavity is treated in some generality using the fluctuation-dissipation theorem. The general line shape of the energy spectrum is derived. This reduces to a Lorentzian when ${\epsilon }^{\prime \prime }\left(\omega \right)$, the imaginary part of the dielectric constant, is small and varies slowly with frequency. Deviations from the Stefan-Boltzmann law are calculated in detail for a cubical cavity.