Reconstruction of a Cold Atom Cloud by Magnetic Focusing

Abstract

We have imaged an $18\ensuremath{\mu}\mathrm{K}$ cloud of ${}^{85}\mathrm{Rb}$ atoms bouncing freely on a horizontal, concave magnetic atom mirror (radius of curvature $R$). A high-quality image is observed even after 14 reflections. Initially compact, the cloud is alternately collimated (odd bounces) and brought back to a focus (even bounces) when dropped from a height $R/4$. This multiple reconstruction of a thermally expanding cloud hinges on the microscopic reversal of the atomic motion. We discuss the factors limiting the resolution of the mirror and describe the method of construction.