This paper investigate how to efficiently focus a cold atomic beam near an atom chip using a two-dimensional magneto-optical trap (2D MOT). We analyze two regimes of atom–laser interaction: Doppler cooling and sub-Doppler cooling.
We show that in the Doppler regime momentum diffusion causes strong heating, so the focusing effect is weak. In contrast, in the sub-Doppler regime the momentum diffusion is much smaller, allowing sharp focusing of the atomic beam and a significant reduction of the beam diameter. As a result, the local density of atoms near the atom chip can increase by more than two orders of magnitude, improving the efficiency of loading atoms into the trapping region for cold-atom devices and quantum sensors.
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