High Resolution Two-Photon Spectroscopy of Rydberg States of Alkaline-Earth Atoms
The investigation of high Rydberg states by means of Doppler-free two-photon spectroscopy using cw dye lasers has opened a new dimension of accuracy. Precise values of ionization limits and quantum defects can be obtained, and the technique is capable of resolving hyperfine structures and isotope shifts[2,3]. In two-electron systems the latter two quantities are sensitive probes of singlet-triplet mixing and perturbations of Rydberg states by other configurations. In this contribution we report on a systematic study of hyperfine structures and isotope shifts of Rydberg states in alkaline-earth elements to elucidate the influence of singlet-triplet mixing and perturbations induced by the hyperfine interaction.