The transfer of spectral line radiation

The physics and mathematics of the interaction of radiation and matter are considered from the standpoint of the physicist wishing to analyze stellar or laboratory spectral line radiation. The qualitative behavior of the radiation field as described by the equation of radiative transfer in a theory for model two-level atoms is addressed, and two distinct methods for the exact solution of that equation are considered. These solutions apply only to constant property media, however, and so a variety of techniques for the numerical solution of the equation are discussed. The model two-level atom approach is generalized to the model multilevel atom. The need to couple the gas-dynamic conservation equations of mass, linear momentum, and energy to the equation of radiative transfer is discussed. The theory of the quantization of the radiation field is used to evaluate relevant atomic parameters and ensemble probabilities. A derivation of the transfer equation using the density matrix formalism of quantum electrodynamics is attempted.