Quantum Properties of Light

In this chapter we discuss the three main empirical phenomena which, for the first time, emphasized the quantum nature of light. These phenomena are the black-body radiation, the photoelectric effect, and the Compton effect. The main idea is that light is made of elementary massless particles called photons. This idea, due to Planck, Einstein, and Compton, is now well established experimentally, and it is the heart of the flourishing field of quantum optics.