Determination of alkali-vapour–inert-gas diffusion coefficients using coherent transient emission from a density grating*

We demonstrate a technique for the accurate measurement of diffusion coefficients for alkali vapor in an inert buffer gas. The measurement was performed by establishing a spatially periodic density grating in isotopically pure ⁸⁷Rb vapor and observing the decaying coherent emission from the grating due to the diffusive motion of the vapor through N₂ buffer gas. We obtain a diffusion coefficient of 0.245 ± 0.002 cm²/s at 50 ^◦C and 564 Torr. Scaling to atmospheric pressure, we obtain D₀ = 0.1819 ± 0.0024 cm²/s*. To the best of our knowledge, this represents the most accurate determination of the Rb-N₂ diffusion coefficient to date. We review progress in extending these measurements to other buffer gases used for magnetometry. These measurements can be used to test calculations of inter-atomic potentials in these systems.

* A. Pouliot et al., Phys. Rev. A 103, 023112 (2021)