Experimental Lifetime Studies of Metastable Levels

Developments in vacuum technology as well as in ion trapping techniques has opened for new possibilities for experimental studies of long-lived metastable states. Since long it has been realized that such levels are of great importance for both fundamental theory and many different kinds of applications. Before the advent of modern technology it was, however, practically impossible to study forbidden transitions from metastable levels in the laboratory. In this review article some of the new experimental methods are briefly described. In particular, the laser probing technique for a stored ion beam developed at CRYRING is described. Recent results for singly charged ions with extremely complex structure are presented. Systematic effects are discussed