Mixing and quenching of the Cs 5 D J states induced by collisions with caesium ground - state atoms ∗

Applying the cw laser absorption and fluorescence method the cross sections for the fine-structure mixing and quenching of the caesium 5DJ states have been measured in pure caesium vapour. Caesium atoms were optically excited to the 5D5/2 state via the quadrupole-allowed 6S1/2 → 5D5/2 transition. The ground-state caesium density N0, obtained from the absorption at the pumped quadrupole transition, and the fluorescence intensity I689 of the sensitized 5D3/2 → 6S1/2 emission were measured simultaneously in the range 3×1014 cm−3 N0 1×1016 cm−3 at constant temperature T = 585 K. It was found that the quantity N2 0 /I689 exhibited a parabolic dependence on N0, confirming that the quenching of the Cs 5DJ states is due to collisions with Cs ground-state atoms, not molecules. The coefficients of the second-order polynomial fitted through the measured data yielded the cross sections σ5/2→3/2 = (57 ± 19) × 10−16 cm2 and σD = (35 ± 10) × 10−16 cm2 for the Cs 5DJ fine-structure mixing and quenching, respectively, due to collisions with caesium ground-state atoms. Using recently calculated Cs∗ + Cs potentials we performed an analysis which shows good agreement between the measured values and the theoretical predictions.