NOBLE-GAS BROADENING RATES FOR THE 6S21S0-]6S6P1,3P1 RESONANCE AND INTERCOMBINATION LINES OF BARIUM

The collisional-broadening and -shift rate coefficients (k(br) and k(shift)), for both helium and argon buffer gases, have been measured in the impact limit for the 6s2S-1(0) --> 6s6pP-3(1) intercombination transition of barium. Detailed absorption line shapes were measured at three different ground-state number densities by monitoring the transmitted intensity of a weak cw probe laser as it was scanned over the transition. A single, density-independent line shape was then constructed and fit to a sum of Voigt functions (to account for hyperfine structure and isotope shifts) in order to determine the broadening and shift rates. By repeating the process for several buffer-gas pressures, k(br) and k(shift) were determined from least-squares straight-line fits to the broadening and shift rates versus buffer-gas number density. Absolute normalization of the line-shape data was used to provide accurate ground-state column densities. Column-density information was then combined with measurements of white-light-absorption equivalent widths for the 6s2S-1(0) -->6s6pP-1(1) resonance transition to yield broadening rates for that transition. These values for the resonance line lie between previous literature values, which are widely discrepant. Finally we measured the absolute metastable 6s5d3D2 column density under conditions of optical pumping through the P-3(1) level, and determined that, in steady state, even with a weak cw pump laser, approximately 20% of all barium atoms in the vapor could be found in the 3D2 level (with approximately 60% spread over the full 3D(J) metastable manifold).