Absorption and Gain Spectra

Abstract

This chapter develops theoretical techniques to describe absorption and emission spectra, using concepts introduced in Chapt. 68, and density matrix methods from Chapt. 7. The simplest cases are treated, compatible with the physics involved, and more realistic applications are referred to in other chapters. Vector notation is not used, but it can be inserted as required. Only steady-state spectroscopy is covered; for time-resolved transient techniques see Chapt. 73. Laser technology has greatly expanded the potential of atomic and molecular spectroscopy, but the same techniques for describing the interaction of light with matter also apply to the traditional arc lamps and flash discharges, and the more recent synchrotron radiation sources.