Precision determination of an excited-state hyperfine splitting of cadmium ions

Precision determination of the hyperfine splitting (HFS) of cadmium ions is useful to study space-time variation of fundamental physical constants and isotope shifts. In this work, we present the precision frequency measurement of the excited-state 2P3/2 hyperfine splitting of 111,113Cd+ ions using the laser-induced fluorescence technique. By introducing the technology of sympathetic cooling and measuring the doublet line transition exploitation of an optical comb system, the uncertainties are improved to 16 and 12 kHz, respectively, two orders of magnitude higher precision than the reported results from the linear transformation of isotope shifts. The magnetic dipole constants AP3/2 of 111Cd+ and 113Cd+ are estimated to be 395 939(8) and 411 275(6) kHz, respectively. The difference between the measured and theoretical hyperfine structure constants indicates that more physical effects are required to be considered in the theoretical calculation and provides critical data for the examination of deviation from King-plot linearity in isotope shifts.