Absorption, Spontaneous Emission, Stimulated Emission, and Maxwell’s Equations*†
Archie I. Mahan
In this paper, four different ways are described in which homogeneous, isotropic, nonferromagnetic, Maxwellian media at rest may exhibit absorption and stimulated emission. These four ways may be identified by a positive or negative conductivity, a sink or source-type electric field, a complex dielectric constant, and a complex permeability. The forms of the electromagnetic waves, the refractive index, and the positive or negative extinction coefficient are determined for each process for both absorbing and active media. Spontaneous emission is associated with source-type electric and magnetic fields which generate conduction or displacement currents in the medium with improper phases to contribute to the radiant flux in the incident electromagnetic wave. Stimulated emission is characterized by exponentially increasing incident electric and magnetic fields and an excess of the time average of the outflow of radiant flux over the surfaces of an arbitrary volume. Stimulated emission appears when the time average of the rate at which the source-type electric and magnetic fields do work in carrying certain conduction or displacement currents in directions opposite to the incident electric and magnetic fields is greater than the time average of the rate at which the incident electric and magnetic fields dissipate energy by doing work in carrying other conduction or displacement currents in directions parallel to the incident electric and magnetic fields.
Journal of the Optical Society of America•Dec 1, 1965•2 citations