The propagation of electromagnetic energy through an absorbing dielectric

Abstract

The energy associated with an electromagnetic wave passing through a dielectric resides partly in the electromagnetic field and partly in the accompanying excitation of the dielectric. The theory of energy propagation through an absorbing classical dielectric having a single resonant frequency is presented in this paper. Simple expressions are derived for the velocity of energy transport associated with an electromagnetic wave, and for the finite energy relaxation time caused by the damping mechanism. The variations of these quantities, and of the absorption coefficient, with the relative values of the damping constant and dipole moment of the classical oscillator are investigated. This information is used to throw light on the basic mechanism of irreversible dissipation of energy by an electromagnetic wave in a dielectric. The similarities between the calculations of the dielectric constant by classical dispersion theory and by quantum mechanics are discussed.