Microscopic Aspects of Weak Light-Matter Coupling

Abstract

The preceding chapter has described the macroscopic properties of light-matter interaction. In this chapter we present the basic interaction processes between light and matter from a microscopic point of view. We use here the perturbative or weak-coupling approach for this interaction, which is in most cases sufficient for dilute systems such as gases. For solids the strong-coupling approach is often necessary. This leads to the concept of polaritons, which is introduced later in Chap. 8. We will first outline the basic interaction mechanisms between light and matter, namely absorption, spontaneous and stimulated emission. Then we proceed to the treatment of linear optical properties in the framework of perturbation theory and derive Fermi’s golden rule.

Problems

6.1

Find in a textbook the definition and meaning of Einstein’s coefficients.

6.2

Inform yourself on time independent perturbation theory. The perturbed wave function contains in first order virtually excited states and the perturbed energy in second order. Inspect time dependent perturbation theory for virtual excitations. Derive Fermi’s golden rule.