Single-laser, one-beam, tetrahedral magneto-optical trap

Shimizu et al. demonstrated an alternative of the usual six beam magneto-optical trap (MOT), using four independent beams in a tetrahedral configuration. This paper demonstrates a novel version of the four beam MOT using a triplet of mirrors to split and steer an incoming beam into three parts such that all four beams cross in the correct configuration. In the usual pyramid configuration, the MOT forms below the top surface of the pyramid and the absence of optical access strongly reduces any manipulation of the cold atomic cloud. In addition, a micro-fabricated tetrahedral configuration offers an ideal tool for a high phase stability optical lattice, with the benefit of fixed lattice geometry. In the demonstration setup, the triplet is positioned underneath the quartz vacuum chamber and its thickness had to be considered. Therefore, the angle of the mirrors is slightly more acute than in the ideal situation, resulting in 45Adeg beams, in order to form the MOT above the plate. Moreover, irect modulation of the diode current by a frequency corresponding to the alkali atom energy splitting in order to generate the repumping light is used. The setup was used to cool down ⁸⁷Rb atoms via the F = 2 and F´ = 3 energy levels of the D2 transition line. With the traditional cooling/repump lasers, 1.3 x 10⁶ atoms were trapped. With a 10mW microwave source, we generated enough repump light into the laser to get 1.1 x 10⁶ atoms, that is 85% compared to the two laser setup.