Optimal Divergent and Elliptical Angle of Gaussian Beams in Trap Relying on Optical Pumping

Abstract. Cooling and trapping neutral atoms is essential for quantum technologies and precision measurement. To cool atoms, lasers can be used to exert forces that slow the motion of the atoms, as if they move inside a dense fluid. Inside a magneto-optical trap (MOT), atoms can be conveniently cooled down to 1mK by superimposing six laser beams in combination with a magnetic field gradient. Recently, a MOT has been realized by delivering divergent light directly from optical fibers to atoms, providing a compact, miniaturizable configuration. It has been shown that this system can further be simplified by removing the magnetic field gradient in a so-called trap relying on optical pumping (TROOP), which achieves confinement using only divergent laser light. To extend the fiber approach to TROOP effectively, we investigate the influence of divergence and polarization angles on trapping behavior and identify the optimal angles. We perform Monte Carlo trajectory simulations of cesium atoms on the Jg = 4 → Je = 5 transition to identify optimal divergent and elliptical angles at fixed initial beam power Iinitial = 1.11×109 W/m2 and find that a beam divergence near 8◦ and perfectly circular polarization maximize trapping stability, whereas for angles smaller than 5◦, the system reflects the behavior of an optical molasses with vanishing confinement.