The Lamb shift in hydrogenic ions

Recent experimental progress and probable future directions in the study of the Lamb shift in high Z hydrogenic ions are reviewed. Advances in techniques and instrumentation have allowed an extension of Lamb shift studies to hydrogenic ions of increasingly higher nuclear charge (Z) using heavy-ion accelerators. New calculational techniques have been applied to high-Z systems. This has stimulated wide interest because the large enhancement that occurs in the Lamb shift due to an approximate Z⁴ dependence allows sensitive studies of QED interactions in the high-field regime and suggests the possibility of observing new and unexpected phenomena. The major experimental methods are the Stark quenching of the metastable 2s_1/2 state in accurately known applied fields and the laser resonance absorption technique. The accuracy of experiments and calculations is considered.