Measurements of Dipole Moments for the 5s5p\,^3\!P_1–5sns\, ^3\!S_1 Transitions via Autler–Townes Spectroscopy

We report on experimental measurements of the transition dipole moments (TDMs) between the intermediate state 5s5p\, ^3\!P_1 and the triplet Rydberg series 5sns\, ^3\!S_1 in an ultracold strontium gas. Here n is the principal quantum number ranging from 19 to 40. The transition 5s5p\, ^3\!P_1–5sns\, ^3\!S_1 is coupled via an ultraviolet (UV) beam, inducing Autler–Townes splitting of both states. Such a splitting of the intermediate state is spectroscopically measured by using absorption imaging on a narrow transition 5s^2\, ^1S_0–5s5p\, ^3\!P_1 in an ultracold gas of strontium atoms. The power and size of the UV beam are carefully determined, with which the TDMs are extracted from the measured Autler–Townes splitting. The experimentally obtained TDMs are compared to the calculations based on a parametric core potential, on a Coulomb potential with quantum defect, and on the open-source library Alkali Ryderg calculator, finding good agreement with the former two models and significant deviation with the latter.