The image (a) shows a 0.4-mm long atom laser beam, generated by extracting atoms from the Bose-Einstein condensate at the top. The atoms in the BEC and the beam are in mF = 0 spin states, making this laser (unlike earlier ones) insensitive to stray magnetic fields. The graph (b) depicts the beam's transverse spread, expected to be limited only by the uncertainty principle. --> to article: PRL 91, 240408 (2003)

Experiment group: Giovanni Cennini, Carsten Geckeler, Gunnar Ritt and Martin Weitz

We have demonstrated an atom laser using all-optical techniques. A Bose-Einstein condensate of rubidium atoms is created by direct evaporative cooling in a quasistatic dipole trap realized with a single, tightly focused CO₂-laser beam. An applied magnetic field gradient allows formation of the condensate in a field-insensitive m_F = 0 spin projection only, which suppresses fluctuations of the chemical potential from stray magnetic fields. A collimated and monoenergetic beam of atoms is extracted from the Bose-Einstein condensate by continuously lowering the dipole trapping potential in a controlled way to form a novel type of atom laser.

Link to Preprint.

Shadow images of the atomic cloud after 15 ms of free expansion (field of view: 0.33 mm). (a) Stern-Gerlach magnetic field gradient applied throughout the experiment, so that a pure m_F = 0 condensate is produced. (b) Field gradient activated only during free expansion phase. The three spin projections m_F = -1, 0 and +1 of a spinor condensate are visible as separate clouds.

Absorption images of atoms extracted from the dipole trap by lowering of the trapping potential: (a) thermal cloud (b) for a Bose-Einstein condensate, where an atom laser beam is formed. The field of view comprises 0.28 mm times 0.5 mm.