Rydberg atoms radiating in free-space or in cavities: new systems to test electrodynamics and quantum optics at an unusual scale

Several review articles have been recently devoted to various aspects of Rydberg atom radiative properties in free space or in cavities. In this course, the main results already discussed in these papers are recalled and some of the most recent developments in this field are discussed. In a first section, the main radiative properties of Rydberg atoms in free space are analyzed and some simple experiments in which these properties have been investigated are mentioned. A second section is devoted to the problem of a single Rydberg atom in a cavity, analyzing the various cavity Q.E.D. effects which have been already observed or are presently being searched for. In a third section, the collective behavior of Rydberg atoms in cavities are discussed and the interesting statistical properties of the atomic and field observables and the possible applications of these systems are described. 64 references, 12 figures