Accurate Determination of an alkali-inert gas diffusion coefficient using coherent transient emission from a density grating

TL;DR

This paper introduces a novel optical technique to precisely measure alkali vapor diffusion coefficients in inert gases, providing highly accurate data crucial for applications in magnetometry and theoretical modeling.

Contribution

The study presents a new method using coherent transient emission from a density grating to measure alkali vapor diffusion coefficients with unprecedented accuracy.

Findings

Measured diffusion coefficient of Rb in N2 at 50°C and 564 Torr.

Scaled diffusion coefficient to atmospheric pressure.

Most accurate Rb-N2 diffusion coefficient to date.

Abstract

We demonstrate a new 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 $^{87}$Rb vapor and observing the decaying coherent emission from the grating due to the diffusive motion of the vapor through N$_2$ buffer gas. We obtain a diffusion coefficient of $0.245 \pm0.002 ~\textrm{cm}^{2}/\textrm{s}$ at 50$\degree$C and 564~Torr. Scaling to atmospheric pressure, we obtain $D_0 = 0.1819 \pm 0.0024~\textrm{cm}^2/\textrm{s}$. To the best of our knowledge, this represents the most accurate determination of the Rb--N$_2$ diffusion coefficient to date. Our measurements can be extended to different buffer gases and alkali vapors used for magnetometry and can be used to constrain theoretical diffusion models for these systems.