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

Published

January 25, 2024

Author(s)

Jeremy Glick, William Huntington, Michael Borysow, Daniel Heinzen, Jacek Klos, Eite Tiesinga

Abstract

We present three-dimensional Monte-Carlo simulations of the capture of 1000 K 7Li or 500 K 87Rb atoms by a continuous supersonic 4He jet and show that intense alkali-metal beams form with narrow transverse and longitudinal velocity distributions. The nozzle creating the 4He jet is held at approximately 4 K. These conditions are similar to those in the cold 7Li source developed by some of us as described in [Phy. Rev. A 107, 013302 (2023)]. The simulations use differential cross-sections obtained from quantum scattering calculations of 7Li or 87Rb atoms with 4He atoms for relative collision energies between k×1 mK to k×3000 K, where k is the Boltzmann constant. For collision energies larger than ≈ k × 4 K the collisions favor forward scattering, deflecting the 7Li or 87Rb atoms by no more than a few degrees. From the simulations, we find that about 1% of the lithium atoms are captured into the 4He jet, resulting in a lithium beam with a most probable velocity of about 210 m/s and number densities on the order of 108 cm−3. Simulations predict narrow yet asymmetric velocity distributions which are verified by comparing to fluorescence measurements of the seeded 7Li atoms. We find agreement between simulated and experimentally measured seeded 7Li densities to be better than 50% across a range of 4He flow rates. We make predictions for capture efficiency and cooling of 87Rb by a supersonic 4He jet. The capture efficiency for 87Rb is expected to be similar to 7Li.

Citation

Physical Review A

Pub Type

Journals

Keywords

supersonic jet, cold atoms, collisions

Citation

Glick, J. , Huntington, W. , Borysow, M. , Heinzen, D. , Klos, J. and Tiesinga, E. (2024), Monte-Carlo simulations of the capture and cooling of alkali-metal atoms by a supersonic helium jet, Physical Review A (Accessed September 11, 2024)