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Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Optical Metrology

KALEXUS - Potassium laser experiments on a sounding rocket

A. Dinkelaker, V. Schkolnik, M. Schiemangk, A. Kenyon, M. Krutzik, A. Peters


See also our publication and the press release on the result of the sounding rocket flight.


Lasers with stable and accurate output frequencies are the key element in high precision experiments such as atom interferometers and atomic clocks. Moreover, future space missions, including quantum based tests of the equivalence principle or the detection of gravitational waves, require such robust and compact lasers with high mechanical and frequency stability.

The KALEXUS (Kalium Laser-Experimente unter Schwerelosigkeit) experiment consists of two narrow linewidth extended cavity diode lasers (ECDLs) [1] for potassium spectroscopy, a Zerodur-based spectroscopy unit as well as miniaturized control and driver electronics. KALEXUS can be seen as a pathfinder experiment to demonstrate the suitability of these lasers and technologies for future quantum sensor experiments in space.


The complete system is part of the payload of a TEXUS sounding rocket, which is a sounding rocket program for research in microgravity by the DLR. It was successfully launched on January 23rd onboard the TEXUS 53 sounding rocket (you can watch the TEXUS 53 launch video).

Throughout the flight, the experiment was designed to function fully autonomously, for which a state-machine based software was developed. Additionally, redundancy architecture was tested during this experiment to provide options for reliable operation for future missions. KALEXUS is complementary to other, related experiments in the Optical Metrology group that have a stronger focus on technology development (e.g. LASUS-I /-II) or on atomic physics experiments (QUANTUS-I/-II/-III).


Here, in the Optical Metrology group by Prof. Achim Peters, Ph.D. at the Humboldt-Universität zu Berlin (HUB), we were responsible for the overall design and the setup of the experiment as a whole. After completion, we developed large parts of the software, got the experiment running and optimized the system’s parameter. The HUB was supported by the Joint Lab "Laser Metrology" (Dr. Andreas Wicht), where the lasers were built and which is run jointly by the Ferdinand-Braun-Institut Berlin and HUB.


Additional support came from the Leibniz Universität Hannover ("Atom Optics and Quantum Sensors" group by Prof. Dr. Ernst M. Rasel), who designed and built the electronics, and from the Johannes Gutenberg Universität Mainz ("Experimental Quantum Optics and Quantum Information" group by  Prof. Dr. Patrick Windpassinger),  where the Zerodur-spectroscopy module was built. There is also a cooperation with Menlo Systems, who will re-fly their experiment FOKUS. This cooperation allows us to compare the emission frequency of the KALEXUS laser with a frequency comb by Menlo Systems [2] and thus independently test the suitability of these lasers for future atomic physics experiments in space.

KALEXUS successfully flew onboard the TEXUS 53 sounding rocket, which launched on Jauanry 23rd 2016, at 8:30 am from the Esrange Space Center in Sweden. The rocket reached a height of 250 km and allowed for 6 minutes of microgravity.

The KALEXUS experiment survived the harsh conditions during start and landing and we successfully operated it in space. We are currently analyzing the data to gain insights into the experiment stability and performance.


You can watch the rocket launch from Esrange here:

TEXUS 53 launch video


Press Release:

Pressemitteilung TEXUS 53 HU Berlin



This work is supported by the German Space Agency DLR with funds provided by the Federal Ministry for Economic Affairs and Energy under grant numbers DLR 50WM 1345.




  • [1] Luvsandamdin et. al., Optics Express, Vol. 22, I. 7, (2014)
  • [2] Wilken T. et al., A frequency comb and precision spectroscopy experiment in space, CLEO2012 in OSA Technical Digest, paper AF2H.5 (2013)




  • aline.dinkelaker(at)physik.hu-berlin.de
  • markus.krutzik(at)physik.hu-berlin.de


The KALEXUS team:


The KALEXUS team

M. Schiemangk, A. Kenyon, A. Dinkelaker, V. Schkolnik, KALEXUS


M. Schiemangk, V. Schkolnik, A. Dinkelaker, A. Kenyon and K. Lampmann (JGU Mainz) in front of the assembled TEXUS 53 payload.