Properties of microelectromagnet mirrors as reflectors of cold Rb atoms

Cryogenically cooled microelectromagnet mirrors were used to reflect a cloud of free-falling laser-cooled ${}^{85}\mathrm{Rb}$ atoms at normal incidence. The mirrors consisted of microfabricated current-carrying Au wires in a periodic serpentine pattern on a sapphire substrate. The fluorescence from the atomic cloud was imaged after it had bounced off a mirror. The transverse width of the cloud reached a local minimum at an optimal current corresponding to minimum mirror roughness. A distinct increase in roughness was found for mirror configurations with an even versus odd number of lines. These observations confirm theoretical predictions.