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 ${}^7\mathrm{Li}$ oder ${}^{87}\mathrm{Rb}$ atoms with ${}^4\mathrm{He}$ atoms for relative collision energies between $k\times 1$ mK and $k\times 3000$ K, where $k$ is the Boltzmann constant. For collision energies higher than approximately $k\times 4$ K the collisions favor forward scattering, deflecting the ${}^7\mathrm{Li}$ oder ${}^{87}\mathrm{Rb}$ 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 $210\mathrm{m}/\mathrm{s}$ and number densities on the order of ${10}^8{\mathrm{cm}}^{-3}$. 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 ${}^7\mathrm{Li}$.

• Received 23 February 2024
• Revised 30 May 2024
• Accepted 29 July 2024

DOI:https://doi.org/10.1103/PhysRevA.110.023114