The renowned Humboldt-Universität zu Berlin, with a history stretching back over 200 years, is one of Germany's eleven Universities of Excellence. Research at the Institute of Physics focuses on elementary particle physics, solid state physics, macromolecules/complex systems and optics/photonics. The Optical Metrology working group needed a clean room workstation for the BECCAL (BoseEinstein Condensate and Cold Atom Laboratory) project, where a laser system is to be developed and built for future research on ultracold atoms on the ISS (International Space Station).

Cooled atoms

What are ultracold atoms? For certain applications, such as atomic clocks, the atoms must not move too quickly. This requires them to be cooled in a highly diluted gas to near absolute zero temperature, which can be achieved using the laser cooling method (Nobel Prize in Physics 1997). This involves irradiating the atoms with precisely tuned laser light so that faster atoms preferentially absorb its photons and are slowed down and cooled by the resulting recoil. The university and the Department of Physics have been relying on the MiniTec profile construction kit for years, as its flexibility makes it ideal for research purposes. Accordingly, MiniTec Berlin was commissioned to realize the workstation in a clean room at the university, which is also based on profiles.

Comprehensive requirements

The requirements for the workstation were diverse. For example, it had to be dissipative to protect against electrostatic discharge (ESD), which was explicitly tested and approved by the university. Furthermore, the centrally located large optical table had to be equipped with special laser protection plates. These are intended to prevent laser beams from leaving the table in an uncontrolled manner. The workstation had to be positioned in the clean room under the FFU (Filter Fan Units) in such a way that the work area could be cleaned by the air flow and not be contaminated by the fans of the devices positioned above the optical table. This is why the baffle plates extend up to 10 mm below the cleanroom ceiling. The 230 V cables for a large number of socket strips also had to be laid individually inside the profiles due to the electrical fuse protection requirements. For this reason, eight entry holes were drilled in the 90x90 L profiles used, followed by a further eight milled holes in the 45x90 profiles at the position of the socket strips. Like the power cables, the network cables were laid "invisibly" behind cable ducts. The challenge here was that the network cables had to be routed through the 45x90 profile in the media duct 1 area. The sheets of the laser protection plates were glass bead blasted to remove the contour of the rolling direction and then anodized matt black. Sufficient space had to be left under the laser protection plates, which are attached to the edge of the optical table as standard, to allow air to flow downwards away from the FFU. Alternatively, the same laser protection plates can also be screwed onto the central area of the optical table in order to separate individual areas for the experiments.