A universal comb
Optical frequency comb allows more accurate astronomical observations.
Scientists from the Leibniz Institute for Astrophysics in Potsdam (AIP) and the Centre for innovation competence innoFSPEC have tested a novel optical frequency comb at an astronomical instrument. This new light source shall improve the calibration of spectrographs and hence their scientific measurements.
"The speciality of the light generated by the optical frequency comb is that it consists of individual, discrete colours, with exact frequency spacing in between," explains the responsible innoFSPEC scientist Jose Boggio. „The optical comb is created by the superposition of laser light with two different frequencies.“ The resulting spectrum is not continuous, as in a rainbow, but consists of different coloured lines with fixed intervals and dark gaps between them - hence the name frequency comb.
As to analyze the light from stars and galaxies, all spectrographs must be calibrated using a known light source. "The frequency comb serves as optical ruler, which is more stable and regular, than the light from conventional spectral 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 in Potsdam, the frequency comb has undergone a first practical test on sky. For an observing campaign at the Calar Alto Observatory in southern Spain, the AIP-built PMAS spectrograph was equiped with the frequency comb. After the successful outcome of these tests, Roger Haynes, head of the innoFSPEC research group, is sure that optical frequency combs will set a new standard in astronomical precision spectroscopy and laboratory analysis.
Already in 2005, Professor Hänsch from the Max-Planck-Institute for quantum optics, received the Nobel Prize for the development of an laser frequency comb. However, the device developed in Potsdam is based on a different principle of operation and produces comb-lines with a larger pitch. This makes it usable for a typical astronomical night-time spectrograph with medium resolution.
The German-Spanish Calar Alto Observatory is located at Sierra de los Filabres, north of Almería (Andalucía, Spain). It is jointly operated by the Instituto Max Planck de Astronomía in Heidelberg, Germany, and the Instituto de Astrofísica de Andalucía (CSIC) in Granada, Spain. Calar Alto has three telescopes with apertures of 1.23m, 2.2m and 3.5m. A 1.5m aperture telescope, also located at the mountain, is operated under control of the Observatorio de Madrid.
COMMUNICATION – CALAR ALTO OBSERVATORY