Velocity dependence of the Cs(5D) + Cs(6P) -> Cs(7D) + Cs(6S) energy pooling process

Qian Wang, Yifan Shen, Kang Dai

Sean Sweeney, John Huennekens, Aaron Marks

王倩, 戴康, 沈异凡

Yifan Shen

Using stepwise excitation of the cesium 8S atoms level in Cs vapor,several collisional and radiative processes have been identified from the intensities and spectra of the Cs fluorescence.The 5D state was populated by 8S→7P→5D transitions.In cesium densities 1016-1017?cm-3,the energy pooling collisions 5D+5D→nL+6S(nL=9D,11S,7F are studied.Since the 5D→6P(3.0-3.6 μm) fluorescence could not be detected with this experiment,the EP rate coefficients have been measured relative to the known rate coefficient of the collision,i.e.,6P+5D→6S+7D.The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode laser beam,tuned to 6P3/2→8S1/2 transition,which could be translated parallel to the pump beam.The excited atom densities are combined with measured fluorescene ratios to determine cross sections for the cesium energy pooling process.The average values(in units of 10-10?cm3s-1) for nL=9D,11S and 7F are 8.4±4.2,7.3±3.6,and 9.7±4.8,respectively.Influence on k11S and k7F of the energy transfer process 11S+6S7F+6S is also dicussed.

Qing Wang, Kang Dai, Yifan Shen

We report experimentally the measured rate coefficients for the energy pooling (EP) collisions process Cs(5D)+Cs(5D)-gCs(6S)+Cs(nL=9D,11S,7F) in cesium densities of 10^(16)-10^(17) cm^(-3). The 5D state was populated via 8S-g7P-g5D spontaneous emission following two-step pumping 6S-g6P_(3/2)-g8S. Since the 5D-g6P (3.0-3.6 microns) fluorescence could not be detected in this experiment, we carried out a relative measurement for the process 6P+5D-g6S+7D. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode laser beam, tuned to 6P_(3/2)-g9S_(1/2) transition, which could be translated parallelly to the pump beam. The excited atom densities have been combined with the measured fluorescence ratios to yield EP rate coefficients. The average values for nL=9D,11S and 7F are 8.0+-4.0, 7.0+-3.5, and 9.3+-4.6 (in units of 10^(-10) cm3/s), respectively. Influence of the energy transfer process 11S+6S-g7F+6S on the rate coefficients k_(11S) and k_(7F) is also discussed.

Yifan Shen

An experimental study of energy transfer collisions, Cs(6P)+Cs(6S)+He→Cs(5D) + Cs(6S)+He, at thermal energies, was carried out in a cell. Atoms were excited to the 6P3/2 state using a single-mode diode laser. The Cs(6P) atom density and spatial distribution were mapped by monitoring the absorption of a counter-propagating laser beam. The buffer gas enhanced the energy transfer between Cs(6P) and Cs(6S), which was based on the measurement of the fluorescence from the 7D state populated by the Cs(6P)/Cs(5D) collisions. Since the 5D→6P fluorescence(3.0-3.6μm) can not be detected with this experiment, the rate coefficient has been measured relative to the known rate coefficient of the collision (i.e., 6P+5D→6S+7D). The three-body collision rate coefficient [k3 = (2.2±1.1)×10-28cm6s-1] is obtained.