A universal comb

10 December 2014. Scientists from the Leibniz Institute for Astrophysics in Potsdam (AIP) and the Centre for innovation competence innoFSPEC have tested a novel optical frequency comb using an astronomical instrument. This new light source will improve the calibration of spectrographs and hence their scientific measurements.
A universal comb

Selected spectrum.

"The special quality of the light generated by the optical frequency comb is that it consists of individual, discrete colours, with a precise frequency spacing," explains the responsible innoFSPEC scientist Jose Boggio. „The optical comb is created by the superposition of laser light with two different frequencies.“ The resulting comb spectrum is not continuous, as in a rainbow, but consists of different coloured lines with fixed spacing and dark gaps between - hence the name frequency comb.

To analyse the light from stars and galaxies, all spectrographs must be calibrated using a known light source. "The frequency comb serves as optical ruler that is more stable and regular, than the light from conventional spectral calibration lamps", explains astrophysicist Andreas Kelz. "Thanks to these methods, we will be able to determine the rotational speeds of galaxies or the chemical composition of stars more precisely."

After development in the laboratories of innoFSPEC Potsdam, the frequency comb has undergone a first practical test on sky. During a recent observing campaign at the Calar Alto Observatory in southern Spain, the AIP-built PMAS spectrograph was equipped with the frequency comb. After the successful outcome of these tests, Roger Haynes, head of the innoFSPEC research group, is sure that laser frequency combs will set new standards in  astronomical precision spectroscopy and laboratory analysis.

Back in 2005, Professor Hänsch from the Max-Planck-Institute for quantum optics, received the Nobel Prize for the development of an optical frequency comb. However, the device developed in Potsdam is based on a different principle of operation and produces comb-lines with a much larger pitch. This makes it applicable for typical astronomical night-time spectrograph operating at low and medium resolution.

Caption: Selected spectrum of the optical frequency comb (upper, blue panel) as compared to a Neon spectral lamp emission (lower red panel). The comb is a better calibrator („optical ruler“), because it features more and equally spaced emission lines than the Neon lamp.


Science contacts:

Dr. Jose Chavez-Boggio, jboggio@aip.de, +49 331-7499 665 / Dr. Andreas Kelz, akelz@aip.de, +49 331-7499 640

Media contact: Kerstin Mork, presse@aip.de, +49 331-7499 469


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.