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Physical Review A

Diffusion of barium atoms in the 6s5d 3 DJ metastable levels and the 6 s2 1 S0 ground state through noble-gas perturbers

R. K. Namiotka, E. Ehrlacher, J. Sagle, M. Brewer, D. J. Namiotka, A. P. Hickman, Alan D. Streater, John Huennekens

Published Jul 1, 1996• 16 citations
Publisher

Abstract

We describe a set of experiments that investigate diffusion of barium 6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$ metastable level and 6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$ ground-state atoms through the noble gases: He, Ne, Ar, Kr, and Xe. The barium metastable levels were populated through optical pumping of the 6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}6s6p${\mathrm{}}^{3}$${\mathit{P}}_{1}^{\mathit{o}}$ intercombination transition with a pulsed laser, followed by spontaneous or stimulated emission into the 6s5d${\mathrm{}}^{3}$${\mathit{D}}_{1,2}$ levels. Collisional mixing then distributed population throughout the 6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$ levels. A weak narrow-band cw laser was tuned to appropriate transitions to probe the spatial distribution of metastable level atoms, as well as the hole created in the ground-state spatial distribution, by the pulsed laser. Time-dependent absorption coefficients were obtained by measuring the transmission of the probe laser at several different pump-probe spatial separations. From these absorption data, spatial number density profiles were mapped out for various times following the firing of the pump laser. These density profiles were used to determine the diffusion coefficient for each state at a particular buffer-gas pressure and temperature. From these pressure- and temperature-dependent diffusion coefficients D, we determined the thermally averaged diffusion cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$) for the metastable and ground-state atoms diffusing through the noble gases, respectively. We also report values for the scaled standard diffusion coefficients ${\mathit{D}}_{0}$. Our experimental values of the thermally averaged diffusion cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$) for the barium-helium system are compared with values calculated from published, theoretical barium-helium potentials and the agreement is excellent. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.54.449

Related papers

Excitation transfer among, and quenching of, the barium 6s5d 3 DJ metastable levels due to collisions with argon, nitrogen, and barium perturbers

E. Ehrlacher, John Huennekens

We describe a set of experiments that investigate excitation transfer among the barium 6s5d $^{3}$${\mathit{D}}_{\mathit{J}}$ metastable levels due to collisions with argon perturber atoms, and quenching of atoms in these levels by nitrogen perturber molecules. The metastable levels were populated through optical pumping of the 6${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}6s6p $^{3}$${\mathit{P}}_{1}^{\mathit{o}}$ intercombination transition with a pulsed laser, followed by stimulated emission or stimulated Raman scattering into the 6s5d $^{3}$${\mathit{D}}_{1,2}$ levels. Collisional mixing then distributed population throughout the $^{3}$${\mathit{D}}_{\mathit{J}}$ levels. Time-dependent absorption coefficients were obtained by measuring the transmission of a weak cw probe laser beam (after the pulsed laser fired) at several perturber number densities. Argon buffer gas was used to investigate fine-structure mixing, and nitrogen was used to study quenching. The time-dependent absorption coefficients were fitted to appropriate fitting functions, obtained by solving the set of coupled rate equations used to model the time evolution of the metastable level populations. The buildup rates of the initially unpopulated $^{3}$${\mathit{D}}_{3}$ and underpopulated $^{3}$${\mathit{D}}_{1}$ levels were used to determine the collisional mixing rates, while the measured decay rates of the $^{3}$${\mathit{D}}_{\mathit{J}}$ level populations yielded the quenching rates. From plots of buildup rates versus argon number density for the $^{3}$${\mathit{D}}_{1,3}$ states, we were able to determine four of the six fine-structure mixing rate coefficients ${\mathit{k}}_{\mathit{i}\mathit{j}}$.The results are ${\mathit{k}}_{12}$=(1.71\ifmmode\pm\else\textpm\fi{}0.18), ${\mathit{k}}_{21}$=(1.39\ifmmode\pm\else\textpm\fi{}0.13), ${\mathit{k}}_{23}$=(1.42\ifmmode\pm\else\textpm\fi{}0.13), and ${\mathit{k}}_{32}$=(1.92\ifmmode\pm\else\textpm\fi{}0.16)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The experiment is not sensitive to the values of ${\mathit{k}}_{13}$ and ${\mathit{k}}_{31}$. Estimated rate coefficients for excitation transfer among the $^{3}$${\mathit{D}}_{\mathit{J}}$ levels due to collisions with barium atoms are ${\mathit{k}}_{21}^{\mathrm{Ba}}$=1.3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and ${\mathit{k}}_{23}^{\mathrm{Ba}}$=5.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. A plot of the population decay rates versus ${\mathrm{N}}_{2}$ number density for each of the three metastable levels yielded the average nitrogen quenching rate coefficient ${\mathit{k}}_{\mathit{q}}$=(3.14\ifmmode\pm\else\textpm\fi{}0.19)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$.

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Optical pumping to the6s5dstates in atomic barium

Edmund G. Myers, C. Bell, P. G. Pappas +1 more

Using a flow apparatus, the time dependence of 6${s}^{2}$ ${\mathrm{}}^{1}$${S}_{0}$--6s6p ${\mathrm{}}^{1}$${P}_{1}$ (553.5 nm) resonance fluorescence in atomic barium has been studied following switch-on of cw laser excitation. It was found that the fluorescence decays with rates as great as 1.3\ifmmode\times\else\texttimes\fi{}${10}^{6}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. Assuming this can be ascribed to the pumping of atoms to the 6s5d ${\mathrm{}}^{1}$D and $^{3}\mathrm{D}$ metastable levels, a value for the sum of the transition probabilities can be extracted.

Physical Review A•Apr 1, 1986•15 citations

Optical Pumping of Neon P23 Metastable Atoms

L. D. Schearer

The $^{3}P_{2}$ metastable atoms of neon have been optically oriented. This represents the first case of the optical pumping of non-$S$ state atoms. The optical-pumping process is described, and depolarization cross sections for collisions with ground-state neon and ground-state helium atoms measured. The cross section for collisional depolarization with helium is 4.30 \ifmmode\pm\else\textpm\fi{} 0.22 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$, and with neon is 166 \ifmmode\pm\else\textpm\fi{} 8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at 300\ifmmode^\circ\else\textdegree\fi{}K. The metastable $^{3}P_{2}$ atoms of Ar and Xe have also been optically pumped. As the polarizability of the noble-gas buffer increases, the collisional depolarization cross section approaches the diffusion cross section.

Physical Review•Apr 5, 1969•26 citations
We describe a set of experiments that investigate diffusion of barium 6s5d{\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}} metastable level and 6{\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0} ground-state atoms through the noble gases: He, Ne, Ar, Kr, and Xe. The barium metastable levels were populated through optical pumping of the 6{\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}\ensuremath{\rightarrow}6s6p{\mathrm{}}^{3}$${\mathit{P}}_{1}^{\mathit{o}} intercombination transition with a pulsed laser, followed by spontaneous or stimulated emission into the 6s5d{\mathrm{}}^{3}$${\mathit{D}}_{1,2} levels. Collisional mixing then distributed population throughout the 6s5d{\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}} levels. A weak narrow-band cw laser was tuned to appropriate transitions to probe the spatial distribution of metastable level atoms, as well as the hole created in the ground-state spatial distribution, by the pulsed laser. Time-dependent absorption coefficients were obtained by measuring the transmission of the probe laser at several different pump-probe spatial separations. From these absorption data, spatial number density profiles were mapped out for various times following the firing of the pump laser. These density profiles were used to determine the diffusion coefficient for each state at a particular buffer-gas pressure and temperature. From these pressure- and temperature-dependent diffusion coefficients D, we determined the thermally averaged diffusion cross sections \ensuremathσD{\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}\ensuremathσD​(6s5d{\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}) and \ensuremathσD{\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}\ensuremathσD​(6{\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}) for the metastable and ground-state atoms diffusing through the noble gases, respectively. We also report values for the scaled standard diffusion coefficients D0{\mathit{D}}_{0}D0​. Our experimental values of the thermally averaged diffusion cross sections \ensuremathσD{\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}\ensuremathσD​(6s5d{\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}) and \ensuremathσD{\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}\ensuremathσD​(6{\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}) for the barium-helium system are compared with values calculated from published, theoretical barium-helium potentials and the agreement is excellent. \textcopyright{} 1996 The American Physical Society.
We describe a set of experiments that investigate excitation transfer among the barium 6s5d 3^{3}3DJ{\mathit{D}}_{\mathit{J}}DJ​ metastable levels due to collisions with argon perturber atoms, and quenching of atoms in these levels by nitrogen perturber molecules. The metastable levels were populated through optical pumping of the 6s2{\mathit{s}}^{2}s2 1^{1}1S0{\mathit{S}}_{0}S0​\ensuremath{\rightarrow}6s6p 3^{3}3P1o{\mathit{P}}_{1}^{\mathit{o}}P1o​ intercombination transition with a pulsed laser, followed by stimulated emission or stimulated Raman scattering into the 6s5d 3^{3}3D1,2{\mathit{D}}_{1,2}D1,2​ levels. Collisional mixing then distributed population throughout the 3^{3}3DJ{\mathit{D}}_{\mathit{J}}DJ​ levels. Time-dependent absorption coefficients were obtained by measuring the transmission of a weak cw probe laser beam (after the pulsed laser fired) at several perturber number densities. Argon buffer gas was used to investigate fine-structure mixing, and nitrogen was used to study quenching. The time-dependent absorption coefficients were fitted to appropriate fitting functions, obtained by solving the set of coupled rate equations used to model the time evolution of the metastable level populations. The buildup rates of the initially unpopulated 3^{3}3D3{\mathit{D}}_{3}D3​ and underpopulated 3^{3}3D1{\mathit{D}}_{1}D1​ levels were used to determine the collisional mixing rates, while the measured decay rates of the 3^{3}3DJ{\mathit{D}}_{\mathit{J}}DJ​ level populations yielded the quenching rates. From plots of buildup rates versus argon number density for the 3^{3}3D1,3{\mathit{D}}_{1,3}D1,3​ states, we were able to determine four of the six fine-structure mixing rate coefficients kij{\mathit{k}}_{\mathit{i}\mathit{j}}kij​.The results are k12{\mathit{k}}_{12}k12​=(1.71\ifmmode\pm\else\textpm\fi{}0.18), k21{\mathit{k}}_{21}k21​=(1.39\ifmmode\pm\else\textpm\fi{}0.13), k23{\mathit{k}}_{23}k23​=(1.42\ifmmode\pm\else\textpm\fi{}0.13), and k32{\mathit{k}}_{32}k32​=(1.92\ifmmode\pm\else\textpm\fi{}0.16)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ cm3{\mathrm{cm}}^{3}cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The experiment is not sensitive to the values of k13{\mathit{k}}_{13}k13​ and k31{\mathit{k}}_{31}k31​. Estimated rate coefficients for excitation transfer among the 3^{3}3DJ{\mathit{D}}_{\mathit{J}}DJ​ levels due to collisions with barium atoms are k21Ba{\mathit{k}}_{21}^{\mathrm{Ba}}k21Ba​=1.3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ cm3{\mathrm{cm}}^{3}cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and k23Ba{\mathit{k}}_{23}^{\mathrm{Ba}}k23Ba​=5.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ cm3{\mathrm{cm}}^{3}cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. A plot of the population decay rates versus N2{\mathrm{N}}_{2}N2​ number density for each of the three metastable levels yielded the average nitrogen quenching rate coefficient kq{\mathit{k}}_{\mathit{q}}kq​=(3.14\ifmmode\pm\else\textpm\fi{}0.19)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ cm3{\mathrm{cm}}^{3}cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$.
We present a time resolved study of excitation transfer processes between the low lying excited states of barium (6s6p 3^{3}3PJ{\mathit{P}}_{\mathit{J}}PJ​, 6s5d 1^{1}1D2{\mathit{D}}_{2}D2​, 6s5d 3^{3}3DJ{\mathit{D}}_{\mathit{J}}DJ​) induced by collisions with noble gases. The transient excited state populations have been measured by means of fluorescence and absorption spectroscopy. Cross sections for spin-changing collisions from 3^{3}3P1{\mathit{P}}_{1}P1​ to 1^{1}1D2{\mathit{D}}_{2}D2​ and from 1^{1}1D2{\mathit{D}}_{2}D2​ to 3^{3}3D3{\mathit{D}}_{3}D3​ as well as for fine-structure mixing within the 3^{3}3D multiplet were obtained by fitting the numerical solution of a seven-state system of rate equations including diffusion to the experimental data. We compare our results to experimental findings for other alkaline earth metals and report an improved value of the lifetime of the 6s6p 3^{3}3P1{\mathit{P}}_{1}P1​ state of barium.
Time-resolved measurements of fluorescence and level populations have been made on barium vapour illuminated by an intense pulse of laser radiation (1 MW cm -2 , 50 ns FWHM) tuned to the resonance transition of Ba I, 6s 2 1 S 0 -6s6p 1 P 1 , at 5535 AA. Barium number densities between 10 13 -10 15 cm -3 were investigated, using a buffer gas of helium at 100 Torr. Fluorescence was measured with two different geometrical arrangements, one allowing partial spatial resolution. In neither case did the observed fluorescence saturate with increasing laser power, although the maximum flux was more than sufficient to burn through the vapour column, as confirmed by transmission measurements. The power loss from the laser beam was found to be compatible with the scattered radiation from the pumped column in the absence of radiation trapping. In contrast to other similar experiments, no significant ionisation was detected (<5%). Time-resolved population measurements by anomalous dispersion on the 6s6p 3 P 2 and 6s5d 1 D 2 metastable levels yielded quenching cross sections for both Ba-Ba and Ba-He collisions, but gave anomalous result for the peak populations. A qualitative explanation of the fluorescence anomaly is proposed on the basis of the AC Stark effect, and it is shown that the same effect can inhibit the onset of stimulated emission to the metastable D levels.
Using a flow apparatus, the time dependence of 6s2{s}^{2}s2 1{\mathrm{}}^{1}1S0{S}_{0}S0​--6s6p 1{\mathrm{}}^{1}1P1{P}_{1}P1​ (553.5 nm) resonance fluorescence in atomic barium has been studied following switch-on of cw laser excitation. It was found that the fluorescence decays with rates as great as 1.3\ifmmode\times\else\texttimes\fi{}106{10}^{6}106 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. Assuming this can be ascribed to the pumping of atoms to the 6s5d 1{\mathrm{}}^{1}1D and 3D^{3}\mathrm{D}3D metastable levels, a value for the sum of the transition probabilities can be extracted.
The 3P2^{3}P_{2}3P2​ metastable atoms of neon have been optically oriented. This represents the first case of the optical pumping of non-SSS state atoms. The optical-pumping process is described, and depolarization cross sections for collisions with ground-state neon and ground-state helium atoms measured. The cross section for collisional depolarization with helium is 4.30 \ifmmode\pm\else\textpm\fi{} 0.22 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ cm2{\mathrm{cm}}^{2}cm2, and with neon is 166 \ifmmode\pm\else\textpm\fi{} 8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ cm2{\mathrm{cm}}^{2}cm2 at 300\ifmmode^\circ\else\textdegree\fi{}K. The metastable 3P2^{3}P_{2}3P2​ atoms of Ar and Xe have also been optically pumped. As the polarizability of the noble-gas buffer increases, the collisional depolarization cross section approaches the diffusion cross section.