Rubidium excited state line shapes from 5 P to 5 D and 7 S broadened by helium

Highlights: • Observed broadening, shift, and asymmetry rates for the Rb and line shapes with He. • Observed broadening rates are approximately 3-6 times larger than for the D${}_1$ line. • Observed shift rates are approximately 10 times larger for transitions to than for transitions to. • Qualitatively compared rates to numerically computed potential energy curves. • Observed two-color two-photon absorption at pressures below 25 Torr. Pump modulated laser absorption spectroscopy was used to measure five excited state line shapes for electric dipole allowed transitions beginning in the Rb $5P$ manifold. Helium was used as the collisional buffer gas, with pressures from 0 to 250 Torr. Center frequency, FWHM, and asymmetry parameters were extracted from the fits and plotted versus pressure to determine rates. Lines terminating in the $5D$ manifold had collisional broadening rates, $\gamma$, of 49.5–54.6 MHz/Torr, collisional shift rates, $\delta$ of less than $\pm 1.3$ MHz/Torr, and asymmetry rates, ${\beta }_0$, of less than $\pm 0.08$ mrad/Torr. Lines terminating in the $7^2{S}_{1/2}$ state showed significantly higher rates, with broadening rates of 109.1–111.0 MHz/Torr, shift rates of 11.5–13.3 MHz/Torr, and asymmetry rates of 0.28–0.47 mrad/Torr. These trends qualitatively match numerically computed difference potentials, which also predict large rates for the $7S$ lines and smaller rates for the $5D$ lines.