Quantisation of the Electromagnetic Field

Abstract

In its interaction with matter, the electromagnetic radiation has a characteristic behaviour by which the absorption and emission processes occur in the form of quanta of energy commonly referred to as photons. These phenomena cannot be described on the basis of the classical theory developed in the previous chapter. They need a specific treatment capable of unifying, within a formally consistent theory, the basic concepts of electromagnetism and quantum mechanics. Such theory, called quantum electrodynamics, was developed starting from 1930 with the contribution of eminent physicists, including Dirac and Feynman. In this chapter we will provide a basic introduction to the formalism, so-called of second quantisation, that is today commonly used in the context of quantum electrodynamics to introduce the concept of photon. The applications of this formalism to describe the interaction between matter and radiation and the study of specific physical processes will be introduced in subsequent chapters (Chaps. 11 and 15).