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arXiv:physics/0701194 · Physical Review A

Heteronuclear ionizing collisions between laser-cooled metastable helium atoms

J. M. McNamara, R. J. W. Stas, W. Hogervorst, W. Vassen

Published Jun 29, 2007• 13 citations
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Abstract

We have investigated cold ionizing heteronuclear collisions in dilute mixtures of metastable $(2\phantom{\rule{0.2em}{0ex}}^{3}S_{1})$ $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ atoms, extending our previous work on the analogous homonuclear collisions [R. J. W. Stas et al., Phys. Rev. A 73, 032713 (2006)]. A simple theoretical model of such collisions enables us to calculate the heteronuclear ionization rate coefficient, for our quasiunpolarized gas, in the absence of resonant light $(T=1.2\phantom{\rule{0.2em}{0ex}}\mathrm{mK})$: ${K}_{34}^{(\mathrm{th})}=2.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}$. This calculation is supported by a measurement of ${K}_{34}$ using magneto-optically trapped mixtures containing about $1\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms of each species, ${K}_{34}^{(\mathrm{exp})}=2.5(8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}$. Theory and experiment show good agreement.

DOI
10.1103/physreva.75.062715

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Scattering and ionizing cross sections and rates are calculated for ultracold collisions between metastable helium atoms using a fully quantum-mechanical close-coupled formalism. Homonuclear collisions of the bosonic 4He∗+4He∗^{4}\mathrm{He}^{*}+^{4}\mathrm{He}^{*}4He∗+4He∗ and fermionic 3He∗+3He∗^{3}\mathrm{He}^{*}+^{3}\mathrm{He}^{*}3He∗+3He∗ systems, and heteronuclear collisions of the mixed 3He∗+4He∗^{3}\mathrm{He}^{*}+^{4}\mathrm{He}^{*}3He∗+4He∗ system, are investigated over the temperature range 1 $\ensuremath{\mu}\mathrm{K}$ to 1 K. Carefully constructed Born-Oppenheimer molecular potentials are used to describe the electrostatic interaction between the colliding atoms, and complex optical potentials to represent loss through ionization from the ${}^{1,3}\mathrm{\ensuremath{\Sigma}}$ states. Magnetic spin-dipole-mediated transitions from the ${}^{5}\mathrm{\ensuremath{\Sigma}}$ state are included and results reported for spin-polarized and unpolarized systems. Comparisons are made with experimental results, previous semiclassical models, and a perturbed single-channel model.
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