Vacuum Pressure Measurements using a Magneto-Optical Trap

We demonstrate that the loading dynamics of an alkali-atom magneto-optical trap (MOT) can be used as a reliable measure of vacuum pressure. This technique could be useful when a conventional pressure gauge is unavailable due to constraints on the vacuum system design. We find that for a MOT loading time $\tau$, the vacuum pressure can be estimated as ($2\times 10^{-8}$ Torr s)/$\tau$. This relation is accurate to within approximately a factor of two over wide variations in trap parameters, background gas composition, and trapped alkali species. At low pressures, the accuracy of the method is limited by losses from two-body elastic collisions within the trap. The loss rate from these collisions varies with the MOT parameters, but typically the method can extend into the $10^{-10}$ Torr range. We will present theoretical and experimental verification of the technique, based on both our own investigations and previous reports in the literature.