Rare-gas-induced broadening and shift of two-photon transitions to intermediate $\mathsf{(n=9{-}14)}$ Rydberg states of atomic thallium *

Abstract

Results of broadening and shift measurements of Doppler-free two-photon lines for transitions from the ground state to the \(\) Rydberg states with intermediate principle quantum numbers of atomic thallium perturbed by rare gases are reported. The rates show a distinct behaviour in this range of principle quantum numbers and significant dependence on the total angular momentum of the upper nP state. The experimental results are compared with calculations using a Van der Waals potential and a superposition of polarization and Fermi potentials. Additionally, broadening and shift rates of the transition Tl 6P3/2-9P3/2 have been measured for quadrupolar as well as for mainly scalar excitation. The rates for both kinds of excitation coincide within the limits of error reflecting the small perturbation of the 6P3/2 state compared to that of the upper 9P3/2 state.