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arXiv:2401.13895 · Physical Review A

Monte Carlo simulations of the capture and cooling of alkali-metal atoms by a supersonic helium jet

Jeremy J. Glick, William Huntington, Michael Borysow, Kevin Wen, Daniel J. Heinzen, Jacek A. Kłos, Eite Tiesinga

Published Aug 27, 2024• 1 citation
arXivHTMLPDF

Abstract

We present three-dimensional Monte Carlo simulations of the capture of 1000 K $^{7}\mathrm{Li}$ or 500 K $^{87}\mathrm{Rb}$ atoms by a continuous supersonic $^{4}\mathrm{He}$ jet and show that intense, cold alkali-metal beams form. The simulations use differential cross sections obtained from quantum scattering calculations of $^{7}\mathrm{Li}$ or $^{87}\mathrm{Rb}$ atoms with $^{4}\mathrm{He}$ atoms for relative collision energies between $k\ifmmode\times\else\texttimes\fi{}1$ mK and $k\ifmmode\times\else\texttimes\fi{}3000$ K, where $k$ is the Boltzmann constant. For collision energies higher than approximately $k\ifmmode\times\else\texttimes\fi{}4$ K the collisions favor forward scattering, deflecting the $^{7}\mathrm{Li}$ or $^{87}\mathrm{Rb}$ atoms by no more than a few degrees. From the simulations, we find that about 1% of the lithium atoms are seeded into the $^{4}\mathrm{He}$ jet, resulting in a lithium beam with a most probable velocity of about $210\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s}$ and number densities on the order of ${10}^{8}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. Simulations predict narrow yet asymmetric velocity distributions which are verified by comparing to fluorescence measurements of the seeded $^{7}\mathrm{Li}$ atoms. We find agreement between simulated and experimentally measured seeded $^{7}\mathrm{Li}$ densities to be better than 50% across a range of $^{4}\mathrm{He}$ flow rates. We make predictions for seeding efficiency and cooling of $^{87}\mathrm{Rb}$ by a supersonic $^{4}\mathrm{He}$ jet. The seeding efficiency for $^{87}\mathrm{Rb}$ is expected to be similar to $^{7}\mathrm{Li}$.

DOI
10.1103/physreva.110.023114

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