A Compact, High-Flux Cold Atom Beam Source
- Friday, 01 June 2012
High atom loading efficiency is important for compact and mobile devices where laser power and space are limited.
The performance of cold atom experiments relying on three-dimensional magneto-optical trap techniques can be greatly enhanced by employing a highflux cold atom beam to obtain high atom loading rates while maintaining low background pressures in the UHV MOT (ultra-high vacuum magneto-optical trap) regions. Several techniques exist for generating slow beams of cold atoms. However, one of the technically simplest approaches is a two-dimensional (2D) MOT. Such an atom source typically employs at least two orthogonal trapping beams, plus an additional longitudinal “push” beam to yield maximum atomic flux.A 2D atom source was created with angled trapping collimators that not only traps atoms in two orthogonal directions, but also provides a longitudinal pushing component that eliminates the need for an additional push beam. This development reduces the overall package size, which in turn, makes the 2D trap simpler, and requires less total optical power. The atom source is more compact than a previously published effort, and has greater than an order of magnitude improved loading performance.
An effective pushing field component was realized by tilting the 2D MOT collimators towards a separate three-dimensional (3D) MOT in ultra-high vacuum. This technique significantly improved 3D MOT loading rates to greater than 8 × 109 atoms/s using only 20 mW of total laser power for the source. When operating below saturation, a maximum efficiency of 6.2 × 1011 atoms/s/W was achieved.
One of the most significant improvements of the present 2D MOT over conventional elliptical-beam 2D MOT designs is the angle of the collimators with respect to the axis of the 2D MOT. Both the horizontal and vertical collimators have been optimized to include forward tilt. Associated retro-mirrors are mounted parallel to the axis of the 2D MOT, thus insuring that the reflected beams are also projected forward at the same angle as the incident beams, effectively resulting in a pushing component with a fraction of the overall laser field in each orthogonal direction. The increased push factor at larger collimator angles is offset by reduced lateral trapping efficiency. It is worth noting that the intrinsic symmetry of a retroreflected beam setup is very robust and simple to use.
The forward-angled collimator method allows for high 2D atomic flux without the need for an additional push laser and associated optical and electronic hardware. This cold atom source maintains very high efficiencies while utilizing a simpler, more compact, and more robust package than previous atom sources. The compact design and efficiency of the current apparatus is suitable for cold atom applications in the laboratory, and especially in mobile devices, including cold atom instruments in space.