Rubidium excited state line shapes from 5P to 5D and 7S broadened by helium. (November 2021) - True, Timothy M.
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. Abstract: Pump modulated laser absorption spectroscopy was used to measure five excited state line shapes for electric dipole allowed transitions beginning in the Rb 5 P 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 5 D manifold had collisional broadening rates, γ, of 49.5–54.6 MHz/Torr, collisional shift rates, δ of less than ± 1.3 MHz/Torr, and asymmetry rates, β 0, of less than ± 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 7 S lines and smaller rates for the 5 D lines.