Pulsed excitation on the two-photon Cs $6{\phantom{\rule{0.16em}{0ex}}}^{2}{S}_{1/2}\ensuremath{\rightarrow}7{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{3/2,5/2}$ transition results in time-resolved fluorescence at 697 and 672 nm. The rates for fine-structure mixing between the $7{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{3/2,5/2}$ states have been measured for helium and argon rare-gas collision partners. The mixing rates are very fast, $1.26\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9} {\mathrm{cm}}^{3}$/atom s for He and $1.52\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10} {\mathrm{cm}}^{3}$/atom s for Ar, driven by the small energy splitting and large radial distribution for the valence electron. The quenching rates are considerably slower, $6.84\ifmmode\pm\else\textpm\fi{}0.09\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$ and $2.65\ifmmode\pm\else\textpm\fi{}0.04\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11} {\mathrm{cm}}^{3}$/atom s for He and Ar, respectively. The current results are placed in context with similar rates for other alkali-metal--rare-gas collision pairs using adiabaticity arguments.
Pulsed excitation on the two-photon Cs 62S1/2\ensuremath→72D3/2,5/2 transition results in time-resolved fluorescence at 697 and 672 nm. The rates for fine-structure mixing between the 72D3/2,5/2 states have been measured for helium and argon rare-gas collision partners. The mixing rates are very fast, 1.26\ifmmode±\else\textpm\fi0.05\ifmmode×\else\texttimes\fi10\ensuremath−9cm3/atom s for He and 1.52\ifmmode±\else\textpm\fi0.05\ifmmode×\else\texttimes\fi10\ensuremath−10cm3/atom s for Ar, driven by the small energy splitting and large radial distribution for the valence electron. The quenching rates are considerably slower, 6.84\ifmmode±\else\textpm\fi0.09\ifmmode×\else\texttimes\fi10\ensuremath−11 and 2.65\ifmmode±\else\textpm\fi0.04\ifmmode×\else\texttimes\fi10\ensuremath−11cm3/atom s for He and Ar, respectively. The current results are placed in context with similar rates for other alkali-metal--rare-gas collision pairs using adiabaticity arguments.
Abstract The rates for fine structure mixing and quenching of the moderately excited 8 2 D 5 / 2 and 8 2 D 3 / 2 states of cesium under collision with argon and the more impulsive helium have been measured, using two-photon pulsed excitation and time-resolved fluorescence techniques. The pressure dependence of the eigenvalues of the rate matrix yields very rapid rate coefficients of 2.6 ± 0.2 × 10 − 9 cm 3 / ( atom s ) for He and 5.2 ± 0.4 × 10 − 10 cm 3 / ( atom s ) for Ar, about two–three times faster than for the Cs 7 2 D 5 / 2 ⇌ 7 2 D 3 / 2 relaxation. The quenching rates are also rapid, 1.07 ± 0.04 × 10 − 10 cm 3 / ( atom s
The collision cross sections for alkali-metal--rare-gas spin orbit mixing between the ${n}^{2}{P}_{3/2}\ensuremath{\rightarrow}{n}^{2}{P}_{1/2}$ levels trend strongly with the Massey parameter, or adiabaticity of the collisions. The strength of the interaction, as characterized by the C6 dispersion coefficient, is a secondary influence on the rates. An analytic expression for the probability of energy transfer in alkali-metal--rare-gas collisions is derived using time-dependent perturbation theory. The model agrees well with a broad literature survey of the observed temperature-dependent cross sections. A simple interaction potential successfully organizes the alkali-metal--rare-gas database. The rates become very large for high-lying states, as the collisions are quite sudden and the radius of the valence electron is large. In contrast, the highly adiabatic cesium 62P mixing rates are six to eight orders of magnitude smaller. The mixing rate for the Rb-He diode pumped alkali laser system varies from $0.20--1.53\phantom{\rule{4pt}{0ex}}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\mathrm{cm}{}^{3}/\mathrm{at}.\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ for T=279−−893K.
We report experimental rate coefficients for the energy-pooling collisions Cs(6P1/2)+Cs(6P1/2)\ensuremath{\rightarrow}Cs(6S1/2)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) and Cs(6P3/2)+Cs(6P3/2)\ensuremath{\rightarrow}Cs(6S1/2)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) where ${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$=7P1/2, 7P3/2, 6D3/2, 6D5/2, 8S1/2, 4F5/2, or 4F7/2. Atoms were excited to either the 6P1/2 or 6P3/2 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 6P1/2\ensuremath{\rightarrow}8S1/2 or 6P3/2\ensuremath{\rightarrow}7D3/2,5/2 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 7P1/2 is populated two to three times more efficiently than 7P3/2 in 1/2-1/2 collisions, but that the 7P fine-structure levels are approximately equally populated in 3/2-3/2 collisions. \textcopyright{} 1996 The American Physical Society.
Excitation transfer between the 62P21 and 62P23 resonance states in cesium, induced by Cs-N2 and Cs-H2 collisions, was observed in the first experiment of its kind, in which techniques of sensitized fluorescence are used to investigate collisional mixing between resonance states of alkali atoms in mixtures with molecular gases. The cesium-vapor-gas system, in which the cesium vapor pressure was low enough to avoid radiation trapping, was irradiated with a single component of the resonance doublet. The fluorescent light, which contained both components of the doublet, was monitored at right angles to the direction of excitation. Measurements of relative intensities of the fluorescent components yielded the following cross sections for excitation transfer and for quenching of resonance radiation. For Cs-N2 collisions: ${Q}_{12}(^{2}P_{\frac{1}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=3.6$ A˚2, ${Q}_{21}(^{2}P_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=16.2$ A˚2, ${Q}_{10}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{1}{2}})=55.2$ A˚2, ${Q}_{20}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=63.5$ A˚2. For Cs-H2 collisions: Q12=6.7A˚2, Q21=29.6A˚2, Q10=11.7A˚2, Q20=6.7A˚2. The large sizes of the excitation-transfer cross sections, which are comparable to the corresponding Cs-Cs cross sections, are attributed to resonances with transitions in the molecules.
A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of Cs(6P1∕2) atoms that have undergone a single hyperfine state-changing collision with Ar. In addition, argon pressure broadening rates and shifts of the cesium $6{P}_{1∕2}({F}^{\ensuremath{'}})\ensuremath{\rightarrow}8{S}_{1∕2}({F}^{\ensuremath{''}})$ transitions have been determined. In the experiment, a single mode, cw Ti:sapphire laser is tuned to line center of the $6{S}_{1∕2}(F=4)\ensuremath{\rightarrow}6{P}_{1∕2}$(${F}^{\ensuremath{'}}=3$ or 4) transition. Then, the frequency of a single mode cw dye laser is scanned over the $6{P}_{1∕2}\ensuremath{\rightarrow}8{S}_{1∕2}$ manifold to probe the populations of the 6P1∕2 hyperfine levels. Absorption of probe laser photons is monitored by detecting $8{S}_{1∕2}\ensuremath{\rightarrow}6{P}_{3∕2}$ fluorescence. The experiment is conducted at room temperature, where the Cs density is low $(n\ensuremath{\sim}3.4\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}\mathrm{atoms}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3})$, and thus the probability of a $\mathrm{Cs}\text{\ensuremath{-}}\mathrm{Cs}$ collision is negligible during the Cs(6P1∕2) radiative lifetime. The Ar pressure is varied from 0 to 1.52Torr, and $\mathrm{Cs}\text{\ensuremath{-}}\mathrm{Ar}$ collisions cause population to be transferred from the directly excited $6{P}_{1∕2}({F}^{\ensuremath{'}})$ level to the other 6P1∕2 hyperfine level. The data are analyzed using a density matrix formalism to yield the rate coefficients for $\mathrm{Cs}(6{P}_{1∕2})\text{\ensuremath{-}}\mathrm{Ar}$ hyperfine state-changing collisions. In addition, the one-dimensional velocity changing collision kernel for Cs(6P1∕2) atoms prepared with vz=0 that undergo ${F}^{\ensuremath{'}}=3\ensuremath{\leftrightarrow}{F}^{\ensuremath{'}}=4$ hyperfine state-changing collisions with argon is reported.
The following cross sections for 92D3/2\ensuremath{\leftrightarrows}92D5/2 fine-structure mixing in Rb, induced in collisions with ground-state Rb and noble-gas atoms, have been measured using methods of atomic fluorescence spectroscopy: Q(92D3/2\ensuremath{\rightarrow}92D5/2) =93, 9, 6, 26, and 42; Q(92D3/2\ensuremath{\leftarrow}92D5/2) =62, 6, 3, 17, and 23, for Rb, He, Ne, Ar, and Kr, respectively, in units of ${10}^{\mathrm{\ensuremath{-}}14}$ cm2. The measured cross sections are in good agreement with recent theoretical calculations of Sirko and Rosi\ifmmode \acute{n}\else \'{n}\fi{}ski.