Rubidium excited state line shapes from 4D-nF (n = 9, 12, 15, 20) broadened by helium

Pump-modulated laser absorption spectroscopy was used to experimentally measure the rubidium $4^2{D}_{5/2}\to n^{2}F$ line shapes broadened by 0-200 Torr of helium. The broadening rates are 175.4$\pm$6.6, 144$\pm$4, 104$\pm$23, and 118$\pm$88 MHz/Torr for $n=9,12,15,20$ respectively, while the shift rates are +36$\pm$8, +113$\pm$5, +143$\pm$19, and +155$\pm$68 MHz/Torr. No asymmetry rates are reported. Broadening rates are seen to decrease slightly with $n$. The direction of the shift is to the blue, as with other Rb–He transitions, and the magnitude of the shift increases with $n$. Stark broadening is observed on the $4D_{5/2}\to 15^{2}F$ and $4D_{5/2}\to 20^{2}F$ transitions at pressures above 10 Torr, with fractional ionization of about 9%.