Quantum Mechanical Background

Abstract

Chapters 1 and 2 describe the interaction of radiation with matter in terms of a phenomenological classical polarization P. The question remains as to when this approach is justified and what to do when it isn’t. Unexcited systems interacting with radiation far from the system resonances can often be treated purely classically. The response of systems near and at resonance often deviates substantially from the classical descriptions. Since the laser itself and many applications involve systems near atomic (or molecular) resonances, we need to study them with the aid of quantum mechanics.