Interaction of Radiation with Atoms and Ions

Abstract

This chapter deals with the interaction of radiation with atoms and ions which are weakly interacting with any surrounding species, such as atoms or ions in a gas phase or impurity ions in an ionic crystal. The somewhat more complicated case of interaction of radiation with molecules or semiconductors will be considered in the next chapter. Since the subject of radiation interaction with matter is, of course, very wide, we will limit our discussion to those phenomena which are relevant for atoms and ions acting as active media. So, after an introductory section dealing with the theory of blackbody radiation, a milestone for the whole of modern physics, we will consider the elementary processes of absorption, stimulated emission, spontaneous emission, and nonradiative decay. They will first be considered within the simplifying assumptions of a dilute medium and a low intensity. Following this, situations involving a high beam intensity and a medium that is not dilute (leading, in particular, to the phenomena of saturation and amplified spontaneous emission) will be considered. A number of very important, although perhaps less general, topics relating to the photophysics of dye lasers, free-electron lasers, and X-ray lasers will be briefly considered in Chaps. 9 and 10 immediately preceding the discussion of the corresponding laser.