Atom–Field Interaction

The interaction of electromagnetic fields with atomic/molecular systems is the genesis of most optical phenomena observed to date. To explain these effects, we need two broad classifications based on both classical and quantum theories. This strategy involves treating (1) fields as classical systems and atoms as quantum systems having discrete energy, (2) fields as quantum systems (particles rather than waves) and atomic systems as classical, or (3) both as quantum systems. Of course, schemes 1 and 2 are easy to solve and visualize, while scheme 3 is the most accurate description but complex in nature. In general, quantum approaches do not lead to exact solutions and require assumptions and simplifications to achieve a reasonably approximate solution. Thus, it is important to choose an appropriate strategy for solving a particular problem. The problem associated with atom–field interactions will also be subjected to different strategies to understand some of the experimentally observed phenomena such as Rabi oscillations. In this chapter, we will derive a master equation that serves as the starting point for solving a large number of problems associated with atom–field interactions.