Magneto-Optical Trap with Millimeter Ball Lenses

We present a magneto-optical trap (MOT) design based on millimeter ball lenses, contained within a metal cube of 19-mm side length. The ball lenses create highly divergent conical MOT trapping beams. In our experiment and in trajectory simulations, we study the effect of beam divergence and light-intensity gradients on MOT performance. We trap approximately 4.2 x 10(5) Rb-85 atoms in our ball-lens MOT at a density of 3.2 x 10(9) cm(-3) and a loading time of 1.3 s. Experimental measurements and the trajectory model are used to calibrate the trapping efficiency in the highly divergent light fields of the ball lenses. The advantages of the design include small lens and chamber sizes favorable to miniaturization, the absence of large-diameter optical-beam pathways, and a low laser-power requirement. These features are conducive to atom-trap geometries with well-defined electromagnetic boundary conditions, as required for ion and plasma traps, and for efficient shielding of black-body and dc stray fields.