ABSTRACT
This chapter describes the interactions between light and matter that are needed to understand how light propagates through matter. It discusses the important case of emission and absorption of radiation by thermal processes, which is referred to as thermal radiation. The chapter focuses on the free electrons and ignore the effect of the positive charges. In addition to absorption, radiation can also be scattered by matter. The chapter focuses on a medium's ability to attenuate radiation by absorbing light. In addition to absorption, radiation can also be scattered by matter. A medium's ability to attenuate radiation will depend on the nature of the particles in the medium and also on the density of these particles. The chapter shows that for thermal radiation the source function is equal to the Planck function, which is the intensity or brightness of a blackbody.
