1. Department of Physics Science and Technology, Xinjiang University, Urumqi 830046, China 2. Department of Mechanical and Electronic Engineering, Northwest A&F University, Yangling 712100, China
Abstract：At a Cs density higher than 9×1014 cm-3, cesium vapor was irradiated in a glass fluorescence cell with pulses of radiation from an YAG-laser-pumped OPO laser, populating 6D5/2 state by two-photon absorption. Energy transfer in Cs6(D5/2)＋Cs(6S) collisions was studied using methods of atomic fluorescence. At the different Cs densities, we have measured the time-integrated intensities of the components and fitted a three-state rate equation model to obtain the cross sections. The experimental points were fitted to a straight line very well. The authors converted the gradient and intercept into cross sections. The cross section for 6D5/2→6D3/2 transfer is (2.1±0.4)×10-14 cm2. The cross section for excitation transfer out of the 6D doublet is σQ=(1.6±0.4)×10-14 cm2. The cross section σQ contains information on reverse energy pooling collisions [i.e., Cs(6D3/2)＋Cs(6S1/2)→Cs(6P)＋6Cs(P)] and contribution from mining in 6DJ→7PJ′, This latter contribution could be subtracted out using the results of a second experiment. At a Cs density lower than 6.0×1012 cm-3, the laser was used to pump the 6D3/2 and 6D5/2 states, respectively. The resulting fluorescence included the direct component emitted in the decay of the 6DJ state and the sensitized component arising from the collisionally populated 7PJ′state. Relative intensities of the components yielded the cross sections. The cross-sections for the processes Cs(6D5/2)＋Cs(6S1/2)→Cs(7PJ′)＋Cs(6S1/2) are (1.6±0.5)×10-15 cm2. for J′=3/2 and (6.5±2.1)×10-16 cm2, for J′=1/2, respectively. The cross-sections for the processes Cs(6D3/2)＋Cs(6S1/2) →Cs(7PJ′)＋Cs(6S1/2) are (1.9±0.6)×10-15 cm2. for J′=3/2 and (7.6±2.4)×10-16 cm2, for J′=1/2, respectively. The 6DJ→7PJ′, energy transfer rate coefficient is small. The total quenching rate coefficient out of the 6DJ state is much larger. Evidence suggests that the quenching of the 6DJ state is caused predominantly by reverse energy-pooling process. The cross section for this process, i.e., Cs(6D3/2)＋Cs(6S1/2)→Cs(6P)＋Cs(6P) is (1.3±0.4)×10-14 cm2.
Key words：Laser spectroscopy;Collisional energy transfer;Fluorescence;Cross section;Cesium
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