Energy-pooling collisions in cesium: 6P_J+6P_J→6S+(nl=7P,6D,8S,4F)

We report experimental rate coefficients for the energy-pooling collisions Cs(6P_1/2)+Cs(6P_1/2)→Cs(6S_1/2)+Cs(nl_J′) and Cs(6P_3/2)+Cs(6P_3/2)→Cs(6S_1/2)+Cs(nl_J′) where nl_J′=7P_1/2, 7P_3/2, 6D_3/2, 6D_5/2, 8S_1/2, 4F_5/2, or 4F_7/2. Atoms were excited to either the 6P_1/2 or 6P_3/2 state using a single-mode Ti:sapphire laser. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode ring dye laser beam, tuned to either the 6P_1/2→8S_1/2 or 6P_3/2→7D_3/2,5/2 transitions, which could be translated parallel to the pump beam. Transmission factors, which describe the average probability that photons emitted within the fluorescence detection region can pass through the optically thick vapor without being absorbed, were calculated for all relevant transitions. Effective lifetimes of levels populated by energy-pooling collisions are modified by radiation trapping, and these factors were calculated using the Molisch theory. These calculated quantities have been combined with the measured excited-atom densities and fluorescence ratios to yield absolute energy-pooling rate coefficients. It was found that the rate for production, in all cases, is greatest for 6D, but that 1/2-1/2 collisions are significantly more efficient than 3/2-3/2 collisions for populating 7P. It was also found that 7P_1/2 is populated two to three times more efficiently than 7P_3/2 in 1/2-1/2 collisions, but that the 7P fine-structure levels are approximately equally populated in 3/2-3/2 collisions. © 1996 The American Physical Society.