Quantization of the Electromagnetic Field. Interaction of Radiation with Matter

G. Grynberg, Alain Aspect, Claude Fabre +1 more

Many processes, including absorption and stimulated emission occurring in lasers, can be handled using a semi-classical model for the atom–radiation interaction, in which the matter is given a quantum description, but the radiation is represented as a classical electromagnetic field (see Chapter 2). There are other phenomena that cannot be adequately described without quantizing the radiation. For example, it has been known since the 1930s that spontaneous emission can only be treated correctly using a fully quantum framework for the interaction, in which both the matter and the radiation are quantized, as we shall see in Chapter 6. However, it was not until the 1970s that situations were found in which a free electromagnetic field , far from sources, exhibited properties and behaviour that could not be described by a classical field, but which could be perfectly well interpreted in terms of a quantized field. This chapter is devoted to the quantization of the free electromagnetic field, far from the charges and currents sourcing it. This free electromagnetic field will be called radiation , and in Chapter 6 we shall specify exactly what is meant by radiation when sources are present. The canonical quantization procedure used here starts from a description of the classical dynamics of the field in the framework of the Hamiltonian formalism, the basic features of which are discussed in Section 4.1.

Прохоров Лев Васильевич

Galina A. Nemova

Constantinos Simserides

The subject of this book is based on the compulsory course "Quantum Optics and Lasers" of the Department of "Solid State Physics" of the Faculty of Physics of the Natural Sciences School of the National and Kapodistrian University of Athens. 1. Introduction to the quantum nature of light. 2. Mechanisms of interaction of electromagnetic (EM) radiation and matter (two-level system). 3. Semiclassical approach of the interaction of EM radiation and matter. EM field: classically. Two-level system e.g. atom: quantum mechanically. 4. Quantum mechanical approach of the interaction of EM radiation and matter. EM field quantization. 5. Lasers. 6. Density matrix. 7. Some other issues for the properties and the operation of Lasers.

Fabrizio Tafuri, C. A. Perroni, G. De Filippis

Gordon Baym

This chapter reviews the classical description of radiation. It describes how classical electromagnetic radiation interacts with a quantum mechanical particle. The general rule is that, even though the wave functions and the electromagnetic potentials change with the gauge, all physically observable quantities are independent of the gauge. The chapter also describes the process of the absorption of light by a system in terms of the effect of an external classical electromagnetic field on the system. The total emission rate is the sum of the induced and the spontaneous rates. Spontaneous emission is just the quantum mechanical version of the classical phenomenon of radiation from an accelerating charge. A very important consequence of the fact that the electromagnetic field is quantized is that there are vacuum fluctuations of the field, analogous to the zero point motion of a harmonic oscillator. Einstein gave a simple statistical argument to determine the rate at which spontaneous emission takes place.