Stark Effect in Two-Electron Atoms by High-Resolution Diode-Laser Spectroscopy

The Stark effect, an interaction between the atom and external electric field, is very important for understanding the atomic structure. Recently, precise theoretical calculations of electric dipole polarizabilities have been reported [1,2]. The electric polarizability is directly related to the atomic wave function, therefore it provides a sensitive test on theoretical calculations. Barium is a heavy two-electron atom. Ytterbium is one of the rare-earth elements and the ground configuration 4f 14 6s 2 and the lower configurations 4f 14 5d6s, 4f 14 6s6p, 4f 14 6s7s can be considered as two-electron configurations. Strong configuration mixing exists in their atomic levels compared with one-electron atoms and yields complicated Stark effect since it results from a configuration mixing between opposite-parity levels [3]. Study of two-electron atoms is, therefore, interesting not only from the spectroscopic point of view but also from the theoretical point of view. Several studies have been reported on the Stark effect in Ba I and Yb I. For Ba, the scalar and tensor polarizabilities of the 6s 2 1 S0 ground state and some states of the 6s5d, 6s6p, and 5d6p configurations were determined [4-6] and, for Yb, these of the 4f 14 6s6p 3 P1 and 1 P1 levels and the 4f 14 6s 2 1 S0  4f 14 6s6p 3 P1 transition were reported [7-9]. Recently, we measured scalar and tensor polarizabilities of the Ba 6s 2 1 S06s6p 3 P1 and Yb 4f 14 6s 2 1 S0  4f 14 6s6p 1 P1 transitions by laser spectroscopy [10,11]. Extending our previous measurements to high lying levels, in this paper we report measurements of Stark shifts for the Ba 6s5d 3 D1 5d6p 3 F2 and Yb 4f 14 6s6p 3 P2  4f 14 6s7s 3 S1 transitions by high-resolution laser spectroscopy. From the measured Stark shifts, the scalar and tensor polarizabilities are determined, and discussed.