Atoms in Static Electric and Magnetic Fields: The Experimental Aspect

Abstract

Thanks to the advent of dye laser in 1971, properties of high lying states of atoms became, relatively soon, one of the forefront topics in atomic physics and numerous experimental studies were undertaken all around the world. These states called “Rydberg states” have few well established characteristics: they have a long life time and a very weak radiative transition probability connects them to the ground state, they are weakly bound, the bending energy varying as 1/n² so that they are very sensitive to external perturbations and in particular to static electric field F and magnetic field B. A small electric field enables the ionization of the Rydberg atoms and thus, offers a very good means to detect them with an efficiency much higher then the current fluorescence detection method. For this reason, electric field ionization process and stark effect of Rydberg states were the first topics to be studied^1,2. On a theoretical point of view the hydrogen was first analyzed and thanks to the separability of the hamiltonian exact numerical solutions were found³ for the spectrum below and above the zero field ionization limit. Nevertheless, there are still some controversies about the structure of the modulated continuum experimentally observed above the threshold; an example of this is reported in this issue (R. J. Damburg). Concerning experiments, at the beginning they have been performed mainly on alkali, for obvious reasons: they are easy to produce in atomic beam, much easy to excite from the ground state than hydrogen etc... However the alkali problem is not entirely identical to the coulomb problem and rapidly the existence of an electronic core has shown to be at the origin of new phenomenons and sometimes very surprising ones which will be described in this text. The problem of non-hydrogenic atoms has been treated in great details by D. A. Harmin⁴ and reported in this issue.