Mixing and quenching of the Cs 5D(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 5D(J) states ha ve been measured in pure caesium vapour. Caesium atoms were optically excit ed to the 5D(5/2) slate via the quadrupole-allowed 6S(1/2) --> 5D(5/2) tran sition. The ground-state caesium density N-0, obtained from the absorption at the pumped quadrupole transition, and the fluorescence intensity I-689 o f the sensitized 5D(3/2) --> 6S(1/2) emission were measured simultaneously in the range 3 x 10(14) cm(-3) less than or equal to N-0 less than or equal to 1 x 10(16) cm(-3) at constant temperature T = 585 K. It was found that the quantity N-0(2)/I-689 exhibited a parabolic dependence on N-0, confirmi ng that the quenching of the Cs 5D(J) states is due to collisions with Cs g round-state atoms, not molecules. The coefficients of the second-order poly nomial fitted through the measured data yielded the cross sections sigma(5/ 2-->3/2) = (57 +/- 19) X 10(-16) cm(2) and sigma(D) = (35 +/- 10) x 10(-16) cm(2) for the Cs 5DJ fine-structure mixing and quenching, respectively, du e to collisions with caesium ground-state atoms. Using recently calculated Cs* + Cs potentials we performed an analysis which shows good agreement bet ween the measured values and the theoretical predictions.