High pressure line shapes of the Rb D1 and D2 lines for 4He and 3He collisions

Abstract

Line shapes for the Rb D1 (5S1/22↔5P1/22) and D2 (5S1/22↔5P3/22) transitions with 4He and 3He collisions at pressures of 500–15,000Torr and temperatures of 333–533K have been experimentally observed and compared to predictions from the Anderson–Talman theory. The ground XΣ1/2+2 and excited AΠ1/22, AΠ3/22, and BΣ1/2+2 potential energy surfaces required for the line shape predictions have been calculated using a one-electron pseudo-potential technique. The observed collision induced shift rates for 4He are dramatically higher for the D1 line, 4.60±0.12MHz/Torr, than the D2 line, 0.20±0.14MHz/Torr. The asymmetry is somewhat larger for the D1 line and has the same sign as the shifting rate. The 3He broadening rate for the D2 line is 4% larger than the 4He rate, and 14% higher for the D1 line, reflecting the higher relative speed. The calculated broadening rates are systematically larger than the observed rates by 1.1–3.2MHz/Torr and agree within 14%. The primary focus of the current work is to characterize the high pressure line shapes, focusing on the non-Lorentzian features far from line center. In the far wing, the cross-section decreases by more than 4 orders of magnitude, with a broad, secondary maximum in the D2 line near 735nm. The potentials do not require empirical modification to provide excellent quantitative agreement with the observations. The dipole moment variation and absorption Boltzmann factor is critical to obtaining strong agreement in the wings.