Unusually large polarizabilities and previously unidentified atomic states in Ba

Abstract

Knowledge of the electric polarizabilities of certain energy levels of barium (not measured in previous studies [1‐10]) is useful for the analysis of experiments with Ba searching for violation of Bose-Einstein statistics for photons [11,12]. We have measured scalar and tensor polarizabilities and some hyperpolarizabilities of four even-parity states (6p 23 P2 ,6 s7d 3 D1,2, and 5d6d 3 D1) of Ba lying between 35 600 and 36 000 cm ˛1 (Fig. 1). Three of these four states have polarizabilities more than two orders of magnitude larger than might be expected from the known energy levels of Ba, implying the existence of two as-yet-unidentified close-lying states of odd parity. Looking for Stark-induced excitations of odd-parity states, we identified transitions to the 6s8p 3 P1 state and to two other states that may be the previously unidentified 6s8p 3 P0,2 states, and measured these states’ energies and polarizabilities. The existence of these states explains the unusually large polarizabilities reported here. Some of the polarizabilities determined in this work are the largest measured for any atomic states with principal quantum number n, 10, with the exception of the nearly degenerate states of hydrogen. Highly polarizable diatomic molecules [13] and Rydberg atoms [14,15] have been used to measure electric fields, for example, in noncontact circuit board testing. The states of Ba studied here could fulfill the same purpose but with a much broader dynamic range. Highly polarizable levels are also of use in experiments searching for (parity and time-reversal violating) atomic electric-dipole moments [16], although the short lifetimes of the levels studied here may limit their usefulness in this regard. Finally, this work demonstrates the use of Starkinduced transitions for the observation of previously unidentified energy levels, a technique that, to our knowledge, has not been previously used for this purpose. Pulsed lasers excite Ba atoms in an atomic beam (Fig. 2) to the even-parity states of interest via two successive E1