Photons: The Motivation to Go Beyond Classical Optics

Many fascinating effects are due to the quantum nature of light; they are the foundation of
quantum optics
. This chapter introduces the concept of the photon as the smallest detectable quantity of light and develops some of the basics required for modelling quantum optics experiments. It shows two examples of images that are typical for the detection of individual photons in one laser beam at very low light intensity. The chapter focuses on the example of light emitted by a broadband thermal source. The classical description provides the tools for describing the statistical properties of light. The measurement of interference, made accessible through the use of instruments such as a Michelson interferometer, clearly demonstrates the wave nature and the coherence properties of light. The nature of the light depends on the type of experiment: a single beamsplitter can often be well described by the photon picture, and a complete interferometer requires the wave picture.