Rydberg atoms and radiation

New Rydberg atom radiative studies, in particular the circular Rydberg states, have special properties which make them particularly suitable for metrological application. A new determination of the Rydberg constant may be obtained by measuring the transition frequency between two adjacing ''circular'' Rydberg states. The authors restrict themselves to a qualitative description of this expanding field. A scheme of an experimental set-up used for Rydberg atom cavity experiments is presented that is quite simple in principle. The Rydberg atoms are prepared by laser excitation of an atomic beam and the laser radiation is attenuated until one makes sure that no more than one atom at a time is prepared in the cavity, etc. This experimental arrangement is also well adapted to the study of collective radiative effects of Rydberg atoms in resonant cavities. This paper shows that Rydberg atom radiation experiments are of interest in a variety of studies not only in fundamental Quantum Optics, but also in the technology of new radiation sources and detectors