Technology from Potsdam for the World’s Largest Telescope

19 November 2013. Two high performance instruments from Potsdam-Babelsberg arrived at the Large Binocular Telescope (LBT) in Arizona, the largest reflector telescope in the world. The so-called PFUs (Permanent Fibre Units) provide both telescope control and the transmission of starlight collected via the telescope mirror to the spectrograph PEPSI (“Potsdam Echelle Polarimetric and Spectroscopic Instrument”)
Technology from Potsdam for the World’s Largest Telescope

The PFUs are mounted at the LBT. (Credit: AIP)

The PFUs were developed and constructed entirely by scientists, engineers and technicians of the Leibniz Institute for Astrophysics Potsdam (AIP) in Babelsberg. The two car-sized control elements were installed on the observation platform of the telescope following their successful transport and delivery to the 3,200-meter altitude location in Arizona. At the end of November, the highly sensitive optics will receive their “first light”. The PFUs will allow the spectrograph PEPSI, which is still being constructed at the AIP workshop, to be operational and available for research from around the world for the first time.

Professor Klaus G. Strassmeier, Head of Project PEPSI & PFU and one of the directors of the AIP: “The two PFUs are designed to lead the starlight from the two 8.4 meter diameter LBT primary mirrors into two microscopically thin fiber optic cables with a diameter of only 0.1 millimeter. In all telescope positions and all weather conditions, every spectrum of light, from ultraviolet to infrared, will flow through the PFUs throughout the entire night without losing a photon – or at least far fewer.”

Three different fiber optic bundles are available for use by researchers and in the end determine the resolution of the PEPSI spectrograph. PEPSI and the two PFUs are able to reach a resolution corresponding to one one-hundredth of the diameter of an atom.

Thanks to the electronic and optical composition of the PFU’s interior, it is also possible to compensate for aberrations caused by the gravitational and thermic deformation of the two large primary mirrors (the so-called “Active Optics”). Additionally, the Potsdam instruments improve the tracking of the telescopes. It is necessary to adjust telescopes, compensating for the rotation of the Earth in order to keep observed objects in focus. PEPSI project scientist Dr. Ilya Ilyin: “In order to guarantee accurate tracing, the PFUs transmit a portion of the collected starlight through an assortment of special beam splitters to two CCD Sensors (Charged Coupled Device)”. The CCD Sensor is a highly sensitive light sensor, which can detect minute changes in brightness and shifts in position and thereby keep the object of stellar observation in focus in “real time”.


Scientific contact: Prof. Dr. Klaus G. Strassmeier, +49 331-7499 223,

Media contact: Kerstin Mork, +49 331-7499 469,


The Large Binocular Telescope (LBT) is located at the Mt. Graham International Observatory in Arizona, USA. The telescope is of a novel design collecting simultaneously the light from the Universe with two circular mirrors, each 8.4m in diameter. The total collecting area of the telescope corresponds to a single circular mirror with a diameter of 11.8m. This makes the LBT the most powerful single mount telescope in the world when it comes to light collection ability. There are also several instruments under development to combine the light from the two mirrors in what is called 'interferometric mode'. This will eventually allow the LBT to achieve images with a resolution about ten times better than the Hubble Space Telescope.


The key topics of the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.