Reconstruction of a cold atom cloud by magnetic focusing

We have imaged an 18 mu K cloud of Rb-85 atoms bouncing freely on a horizon tal, concave magnetic atom mirror (radius of curvature R). A high-quality i mage is observed even after 14 reflections. Initially compact, the cloud is alternately collimated (odd bounces) and brought back to a focus (even bou nces) when dropped from a height R/4. This multiple reconstruction of a the rmally expanding cloud hinges on the microscopic reversal of the atomic mot ion. We ddiscuss the factors limiting the resolution of the mirror and desc ribe the method of construction. [S0031-9007(98)08251-9].