Hyperfine constants and line separations for the S01−P13 intercombination line in neutral ytterbium with sub-Doppler resolution

Abstract

Optical frequency measurements of the intercombination line (6s 2 ) 1 S0 −(6s6p) 3 P1 in the isotopes of ytterbium are carried out with the use of sub-Doppler fluorescence spectroscopy on an atomic beam. A dispersive signal is generated to which a master laser is locked, while frequency counting of an auxiliary beat signal is performed via a frequency comb referenced to a hydrogen maser. The relative separations between the lines are used to evaluate the 3 P1-level magnetic dipole and electric quadrupole constants for the fermionic isotopes. The center of gravity for the 3 P1 levels in 171 Yb and 173 Yb are also evaluated, where we find significant disagreement with previously reported values. These hyperfine constants provide a valuable litmus test for atomic many-body computations in ytterbium.

Isotope shifts for ${}^1S_0-{}^3P_{0,1}^o$ Yb lines from multi-configuration Dirac-Hartree-Fock calculations

“…The computed isotope shifts for the intercombination line are presented in Table III. These values differ on average by 11.5% when compared with measured values from [72]. This difference may reduce with the inclusion of deeper core-valence correlations and possibly core-core correlations [28,48,68].…”

“…For J = 1, the off-diagonal hyperfine constant B(J, J − 1) is vanishing. The hyperfine constants calculated using the rhfs program in the grasp2018 package [48] and are presented in Calculation of the centroid shift using (6) makes use of the energy difference between the fine-structure levels, 3 P o 0 and 3 P o 1 ; i.e., the value of 21 092 574.882(93) MHz for 174 Yb, based on measurements presented in [72] and [81]. The centroid shifts for the clock transition, to second-order in perturbation theory, for the mixing of the 3 P 0 and 3 P 1 states we calculate to be −0.537(44) MHz and −0.476(39) MHz for 171 Yb and 173 Yb, respectively.…”

“…The centers of gravity for the intercombination line isotope shifts presented in [72] are correct to first-order in perturbation theory; however, the second-order corrections due to mixing with the 3 P o 0 state are greater than the experimental uncertainty and so are accounted for here. The effects of mixing with other nearby states ( 1 P o 1 , 3 P o 2 ) are estimated to be less than experimental uncertainty.…”

“…Uncertainties are taken to be 4% by comparison of the diagonal hyperfine constants with the experimental values from Atkinson et al[72].…”

Intercombination line frequencies in $^{171}$Yb validated with the clock transition

“…We are further motivated to test the validity of previous measurements that employed a hydrogen maser as a frequency reference. Atkinson et al [16] made use of absolute frequencies, but the only published value was for isotope 176 Yb. In this previous work we carried out isotope shift spectroscopy on the 1 S 0 − 3 P 1 ICL across all the naturally occurring isotopes (and hyperfine levels).…”