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arXiv:physics/9908038 · Physical Review A

Properties of microelectromagnet mirrors as reflectors of cold Rb atoms

Marija Drndić, Gary Zabow, C. S. Lee, Joseph H. Thywissen, Kent S. Johnson, Mara Goff Prentiss, Robert M. Westervelt, P. D. Featonby, V. Savalli, Laurent Cognet, Kristian Helmerson, Nathalie Westbrook, Christoph Ira Westbrook, William D. Phillips, Alain Aspect

Published Nov 1, 1999• 21 citations

Abstract

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.

DOI: 10.1103/physreva.60.4012

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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.

We have measured the magnitude and roughness of the reflecting potential produced by a current-carrying magnetic mirror from which cold rubidium atoms have been bounced at normal incidence. By varying the current in the mirror, a study of the potential barrier from which the atoms in different magnetic substates bounce has been made. A combination of time-of-flight and imaging techniques allowed us to study the roughness of the reflecting potential. We have demonstrated that the observed roughness can be reduced by additional wires to compensate for the finite-size effects, and by careful control of the direction of the magnetic bias field.

We have deflected a beam of metastable helium atoms using the inhomogeneous magnetic field above a microfabricated electromagnet mirror. The mirror consisted of a single current-carrying wire in a periodic serpentine pattern on a planar sapphire substrate. A time-dependent current (and magnetic field) synchronized with a pulsed thermal atomic beam was used to compensate for the chromaticity of the deflection. The freedom to fabricate a wide variety of geometries and to employ time-dependent fields make microelectromagnets promising new tools for atom manipulation.

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.

We report recent progress on the development of magnetic mirrors for reflecting beams of slowly moving neutral atoms. Different approaches for constructing periodic magnetic structures with micron-scale periodicities are described, including the use of arrays of current-carrying wires fabricated by photolithography, grooved ferromagnetic structures fabricated by electron-beam lithography, and magnetic structures recorded on magneto-optical film by a focused diode laser beam. Results on the reflection of free-falling laser-cooled caesium atoms from these microfabricated magnetic mirrors are presented.

Micro-electromagnets for atom manipulation have been constructed, including magnetic mirrors (serpentine patterns) and traps (circular patterns). They consist of planar micron-scale Au wires on sapphire substrates fabricated using lithography and electroplating. At liquid nitrogen or helium temperatures in vacuum the wires support currents of several amperes with current density ∼108 A/cm2 and power dissipation ∼10 kW/cm2, and they produce magnetic fields to 0.3 T and gradients to 103 T/cm. The micro-electromagnet mirror was used to deflect a beam of metastable helium atoms at grazing angles ∼0.5 mrad.