Enhancement of Phase Space Density by Increasing Trap Anisotropy in a Magneto-Optical Trap with a Large Number of Atoms

The phase space density of dense, cylindrical clouds of atoms in a 2D magneto-optic trap is investigated. For a large number of trapped atoms ($>{10}^{8}$), the density of a spherical cloud is limited by photon reabsorption. However, as the atom cloud is deformed to reduce the radial optical density, the temperature of the atoms decreases due to the suppression of multiple scattering leading to an increase in the phase space density. A density of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ has been achieved in a magneto-optic trap containing $2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms.