Proceedings Article | 12 July 2023
KEYWORDS: Optical benches, Bragg cells, Chemical species, Spectroscopy, Quantum optics experiments, Vibration, Camera shutters, Optical mounts, Zerodur, Rockets
Quantum-optical experiments situated in a gravitationally bound experimental setup are fundamentally limited in numerous ways, such as the gravitational sag experienced by the trapped atoms or the limited free-evolution times of an atomic interferometer. These constraints can be overcome by deploying the experiment in a micro-gravity platform, such as the International Space Station (ISS). The Bose-Einstein Condensate and Cold Atom Laboratory (BECCAL), a collaboration between NASA and DLR and successor to NASA’s CAL mission, aims to achieve just that. Planned as a multi-user experimental facility, it will enable numerous quantum-optical experiments with ultracold atomic clouds of different isotopes of rubidium and potassium in the microgravity environment of the ISS. The optical capabilities of this experiment will be manifold: Atoms can be cooled and trapped using a 2D- and 3D-magneto optical trap (MOT). They can then be loaded into a red-detuned crossed optical dipole trap. Using blue-detuned light, arbitrary painted optical potentials can be applied. Atom interferometry along two separate interferometry axes is also possible. Fluorescence and absorption detection are available for imaging of the atomic ensemble. In this paper, we present a compact and robust optical distribution system which is required to enable this functionality. To this end, we use a combination of fiber-to-fiber coupled optical benches, and fiber-based components. This distribution system needs to withstand the vibrational loads during launch to the ISS, and needs to retain a good fiber-to-fiber coupling efficiency under varying environmental conditions, such as temperature fluctuations, without maintenance, through the multi-year mission time. We have designed a total of ten optical benches, eight for light distribution and two as spectroscopic units. The optical benches make use of our micro-optical bench toolkit based on the glass-ceramic Zerodur, which has mechanical properties akin to aluminium and a negligible coefficient of thermal expansion. The toolkit has been flight-tested in various sounding rocket-missions like KALEXUS, FOKUS, MAIUS-1 and will be used in the upcoming MAIUS-2/3 missions. However, as the size and weight budget are more constrained for BECCAL than for previous missions, we had to further compactify the system by mounting optical components on both sides of the optical benches. As these advancements require verification, we have constructed a number of scientific demonstrators, which have undergone rigorous testing.
